path: root/profiles/use.local.desc

# Copyright 1999-2010 Gentoo Foundation.
# Distributed under the terms of the GNU General Public License v2
# $Header: /var/cvsroot/gentoo-x86/profiles/use.local.desc,v 1.6228 2010/12/17 18:52:45 robbat2 Exp $
# This file contains descriptions of local USE flags, and the ebuilds which
# contain them.
# Keep it sorted (use "LC_ALL=C sort -t: -k1,1 -k2 | LC_ALL=C sort -s -t/ -k1,1")
# Declaring the locale for the sort is critical to avoid flapping.
###########
## NOTICE!!
###########
# This file is deprecated as per GLEP 56 in favor of metadata.xml. Please add
# your descriptions to your package's metadata.xml ONLY.
# use.local.desc is now generated automatically, and manual editing of it is
# disallowed.
# Test for commit block

app-accessibility/brltty:api - build brltty's application program interface
app-accessibility/brltty:beeper - support the console tone generator
app-accessibility/brltty:contracted-braille - support in-line contracted braille
app-accessibility/brltty:fm - support for the sound card synthesizer
app-accessibility/brltty:learn-mode - support for interactive command learn mode
app-accessibility/brltty:midi - support the musical instrument digital interface
app-accessibility/brltty:pcm - support for sound card digital audio
app-accessibility/brltty:pm - user customization of Papenmeier driver
app-accessibility/brltty:speech - speech support
app-accessibility/eflite:16k_voice - Use a higher-quality voice.
app-accessibility/emacspeak:espeak - Adds support for the espeak tts engine
app-accessibility/festival:mbrola - Adds support for mbrola voices
app-accessibility/festival-it:mbrola - Adds support for mbrola voices
app-accessibility/freetts:jsapi - build Java Speech API (JSAPI)
app-accessibility/freetts:mbrola - Adds support for mbrola voices
app-accessibility/gnome-speech:espeak - Adds support for the espeak speech driver (default)
app-accessibility/gnome-speech:festival - Adds support for the festival speech driver
app-accessibility/gnome-speech:freetts - Adds support for the freetts speech driver
app-accessibility/speech-dispatcher:espeak - Adds support for espeak speech engine
app-accessibility/speech-dispatcher:flite - Adds support for flite speech engine
app-admin/bcfg2:server - Installs scripts to be used on the server-side of this app
app-admin/collectd:collectd_plugins_apache - Build the apache input plugin (transferred bytes, handled requests, detailed scoreboard statistics)
app-admin/collectd:collectd_plugins_apcups - Build the apcups input plugin (UPS charge, load, input/output/battery voltage, etc.)
app-admin/collectd:collectd_plugins_ascent - Build the ascent input plugin (statistics about a free server for World of Warcraft)
app-admin/collectd:collectd_plugins_battery - Build the battery input plugin (charge, current and voltage of ACPI and PMU based laptop batteries)
app-admin/collectd:collectd_plugins_bind - Build the bind input plugin (name server and resolver statistics)
app-admin/collectd:collectd_plugins_conntrack - Build the conntrack input plugin (number of nf_conntrack entries)
app-admin/collectd:collectd_plugins_contextswitch - Build the contextswitch input plugin (number of context switches done by the operating system)
app-admin/collectd:collectd_plugins_cpu - Build the cpu input plugin (time spent in the system, user, nice, idle, and related states)
app-admin/collectd:collectd_plugins_cpufreq - Build the cpufreq input plugin (CPU frequency, for laptops with speedstep or similar)
app-admin/collectd:collectd_plugins_csv - Build the csv output plugin (write to comma separated values (CSV) files)
app-admin/collectd:collectd_plugins_curl - Build the curl input plugin (parse statistics from websites using regular expressions)
app-admin/collectd:collectd_plugins_curl_xml - Build the curl_xml input plugin (get xml data via curl and parse it)
app-admin/collectd:collectd_plugins_dbi - Build the dbi input plugin (execute SQL statements on databases and interpret the reply)
app-admin/collectd:collectd_plugins_df - Build the df input plugin (mountpoint usage)
app-admin/collectd:collectd_plugins_disk - Build the disk input plugin (sectors read/written, number of read/write actions, average completion time of IO-operations)
app-admin/collectd:collectd_plugins_dns - Build the dns input plugin (collects statistics of your DNS traffic on port udp/53)
app-admin/collectd:collectd_plugins_email - Build the email input plugin (opens a UNIX domain socket and starts accepting connections on that socket)
app-admin/collectd:collectd_plugins_entropy - Build the entropy input plugin (available entropy on a system)
app-admin/collectd:collectd_plugins_exec - Build the exec input/output plugin (executes scripts / applications and reads values back)
app-admin/collectd:collectd_plugins_filecount - Build the filecount input plugin (countd the number of files in a directory and all its subdirectories)
app-admin/collectd:collectd_plugins_fscache - Build the fscache input plugin (information about the caching infrastructure for network file-systems etc)
app-admin/collectd:collectd_plugins_gmond - Build the gmond input plugin (receive data from gmond, the client daemon of the Ganglia project)
app-admin/collectd:collectd_plugins_hddtemp - Build the hddtemp input plugin (temperature of hard disks)
app-admin/collectd:collectd_plugins_interface - Build the interface input plugin (information about traffic, packets and errors of interfaces)
app-admin/collectd:collectd_plugins_ipmi - Build the ipmi input plugin (read hardware sensors from servers using the Intelligent Platform Management Interface (IPMI))
app-admin/collectd:collectd_plugins_iptables - Build the iptables input plugin (statistics from a ip_tables based packet filter)
app-admin/collectd:collectd_plugins_irq - Build the irq input plugin (number of times each interrupt has been handled by the os)
app-admin/collectd:collectd_plugins_java - Build the java input plugin (embeds a JVM into collectd for writing plugins)
app-admin/collectd:collectd_plugins_libvirt - Build the libvirt input plugin (statistics about virtualized guests on a system)
app-admin/collectd:collectd_plugins_load - Build the load input plugin (system load)
app-admin/collectd:collectd_plugins_logfile - Build the logfile output plugin (writes log messages to a text file)
app-admin/collectd:collectd_plugins_madwifi - Build the madwifi input plugin (information about Atheros wireless LAN chipsets)
app-admin/collectd:collectd_plugins_match_empty_counter - Build the match_empty_counter filter plugin
app-admin/collectd:collectd_plugins_match_hashed - Build the match_hashed filter plugin
app-admin/collectd:collectd_plugins_match_regex - Build the match_regex filter plugin
app-admin/collectd:collectd_plugins_match_timediff - Build the match_timediff filter plugin
app-admin/collectd:collectd_plugins_match_value - Build the match_value filter plugin
app-admin/collectd:collectd_plugins_mbmon - Build the mbmon input plugin (information from mainboard sensors)
app-admin/collectd:collectd_plugins_memcachec - Build the memcachec input plugin (connects to a memcached server)
app-admin/collectd:collectd_plugins_memcached - Build the memcached input plugin (connects to a memcached daemon)
app-admin/collectd:collectd_plugins_memory - Build the memory input plugin (physical memory utilization)
app-admin/collectd:collectd_plugins_multimeter - Build the multimeter input plugin (reads a voltage or current from a multimeter connected to a serial bus)
app-admin/collectd:collectd_plugins_mysql - Build the mysql input plugin (connects to an MySQL-database and issues a SHOW STATUS command)
app-admin/collectd:collectd_plugins_netlink - Build the netlink input plugin (opens a netlink socket to the Linux kernel for getting statistics)
app-admin/collectd:collectd_plugins_network - Build the network input/output plugin (communicates with other instances of collectd)
app-admin/collectd:collectd_plugins_nfs - Build the nfs input plugin (usage of the Network File System)
app-admin/collectd:collectd_plugins_nginx - Build the nginx input plugin (number of requests handled by the nginx daemon)
app-admin/collectd:collectd_plugins_notify_desktop - Build the notify_desktop output plugin (uses libnotify to display notifications to the user)
app-admin/collectd:collectd_plugins_notify_email - Build the notify_email output plugin (uses libESMTP to send notifications to a configured email address)
app-admin/collectd:collectd_plugins_ntpd - Build the ntpd input plugin (queries an NTP server)
app-admin/collectd:collectd_plugins_olsrd - Build the olsrd input plugin (reads information about the Optimized Link State Routing daemon)
app-admin/collectd:collectd_plugins_onewire - Build the onewire input plugin (collects temperature information from sensors)
app-admin/collectd:collectd_plugins_openvpn - Build the openvpn input plugin (reads the status file printed by OpenVPN)
app-admin/collectd:collectd_plugins_oracle - Build the oracle input plugin (SQL-queries one or more Oracle database systems)
app-admin/collectd:collectd_plugins_perl - Build the perl language binding plugin (embeds a Perl interpreter into collectd for writing plugins)
app-admin/collectd:collectd_plugins_ping - Build the ping input plugin (measures network latency)
app-admin/collectd:collectd_plugins_postgresql - Build the postgresql input plugin (connects to and executes SQL statements on a PostgreSQL database)
app-admin/collectd:collectd_plugins_powerdns - Build the powerdns input plugin (connects to a local PowerDNS instance)
app-admin/collectd:collectd_plugins_processes - Build the processes input plugin (statistics about processes)
app-admin/collectd:collectd_plugins_protocols - Build the protocols input plugin (network protocols)
app-admin/collectd:collectd_plugins_python - Build the python language binding plugin (embeds a Python interpreter into collectd for writing plugins)
app-admin/collectd:collectd_plugins_rrdcached - Build the rrdcached input/output plugin (connects to rrdcached and submits updates for RRD files)
app-admin/collectd:collectd_plugins_rrdtool - Build the rrdtool output plugin (writes values to RRD-files)
app-admin/collectd:collectd_plugins_sensors - Build the sensors input plugin (uses lm-sensors to read hardware sensors)
app-admin/collectd:collectd_plugins_serial - Build the serial input plugin (collects the traffic on serial interfaces)
app-admin/collectd:collectd_plugins_snmp - Build the snmp input plugin (read values from network devices using SNMP)
app-admin/collectd:collectd_plugins_swap - Build the swap input plugin (amount of memory currently written to swap)
app-admin/collectd:collectd_plugins_syslog - Build the syslog output plugin (receives messages from collectd and dispatches them to syslog)
app-admin/collectd:collectd_plugins_table - Build the table input plugin (parses table-like structured plain text)
app-admin/collectd:collectd_plugins_tail - Build the tail input plugin (follows logfiles as e.g. tail -f)
app-admin/collectd:collectd_plugins_target_notification - Build the target_notification filter plugin
app-admin/collectd:collectd_plugins_target_replace - Build the target_replace filter plugin
app-admin/collectd:collectd_plugins_target_scale - Build the target_scale filter plugin
app-admin/collectd:collectd_plugins_target_set - Build the target_set filter plugin
app-admin/collectd:collectd_plugins_tcpconns - Build the tcpconns input plugin (number of TCP connections to or from a specified port)
app-admin/collectd:collectd_plugins_teamspeak2 - Build the teamspeak2 input plugin (collects traffic statistics from a teamspeak2 instance)
app-admin/collectd:collectd_plugins_ted - Build the ted input plugin (connects to The Energy Detective and reads the current power over connected power lines)
app-admin/collectd:collectd_plugins_thermal - Build the thermal input plugin (ACPI thermal zone information)
app-admin/collectd:collectd_plugins_tokyotyrant - Build the tokyotyrant input plugin (number of records and file size from a running Tokyo Tyrant server)
app-admin/collectd:collectd_plugins_unixsock - Build the unixsock output plugin (opens a UNIX domain socket and accepts connections)
app-admin/collectd:collectd_plugins_uptime - Build the uptime input plugin (system uptime)
app-admin/collectd:collectd_plugins_users - Build the users input plugin (number of users currently logged in)
app-admin/collectd:collectd_plugins_uuid - Build the uuid plugin (tries hard to determine the UUID of the system it is running on)
app-admin/collectd:collectd_plugins_vmem - Build the vmem input plugin (information about the virtual memory subsystem)
app-admin/collectd:collectd_plugins_vserver - Build the vserver input plugin (virtual servers running on a system)
app-admin/collectd:collectd_plugins_wireless - Build the wireless input plugin (signal quality, signal power and signal-to-noise ratio for wireless LAN cards)
app-admin/collectd:collectd_plugins_write_http - Build the write_http output plugin (sends the values collected by collectd to a web-server)
app-admin/collectd:contrib - Install user-contributed files in the doc directory
app-admin/conky:apcupsd - enable support for sys-power/apcupsd
app-admin/conky:audacious - enable monitoring of music played by media-sound/audacious
app-admin/conky:eve - enable support for the eve-online skill monitor
app-admin/conky:iostats - enable support for per-task I/O statistics
app-admin/conky:lua - enable if you want Lua scripting support
app-admin/conky:lua-cairo - enable if you want Lua Cairo bindings for Conky (also enables lua support)
app-admin/conky:lua-imlib - enable if you want Lua Imlib2 bindings for Conky (also enables lua and imlib support)
app-admin/conky:math - enable support for glibc's libm math library
app-admin/conky:moc - enable monitoring of music played by media-sound/moc
app-admin/conky:mpd - enable monitoring of music controlled by media-sound/mpd
app-admin/conky:nano-syntax - enable syntax highlighting for app-editors/nano
app-admin/conky:nvidia - enable reading of nvidia card temperature sensors via media-video/nvidia-settings
app-admin/conky:portmon - enable support for tcp (ip4) port monitoring
app-admin/conky:thinkpad - enable support for IBM/Lenovo notebooks
app-admin/conky:weather-metar - enable support for metar weather service
app-admin/conky:weather-xoap - enable support for metar and xoap weather service
app-admin/conky:xmms2 - enable monitoring of music played by media-sound/xmms2
app-admin/diradm:automount - Support for automount data in LDAP
app-admin/diradm:irixpasswd - Support for storing separate IRIX passwords
app-admin/gkrellm:X - Build both the X11 gui (gkrellm) and the server (gkrellmd). Disabling this flag builds the server only.
app-admin/gkrellm:gnutls - Enable SSL support for mail checking with net-libs/gnutls (overrides 'ssl' USE flag)
app-admin/gkrellm:hddtemp - Enable monitoring harddrive temperatures via app-admin/hddtemp
app-admin/gkrellm:lm_sensors - Enable monitoring sensors via sys-apps/lm_sensors
app-admin/gkrellm:ntlm - Enable NTLM authentication for mail checking with net-libs/libntlm
app-admin/gkrellm:ssl - Enable SSL support for mail checking with dev-libs/openssl
app-admin/gnome-system-tools:nfs - Adds support for NFS shares
app-admin/hddtemp:network-cron -  Monthly cronjob to update hddtemp.db. 
app-admin/lcap:lids - If you have the Linux Intrusion Detection System
app-admin/prelude-manager:tcpwrapper - Add support for tcp_wrappers
app-admin/puppet:augeas - Enable augeas support
app-admin/puppet:rrdtool - Enable rrdtool support
app-admin/puppet:shadow - Enable shadow support
app-admin/rsyslog:extras - Add support for the UDP spoofing module (omudpspoof) using net-libs/libnet
app-admin/rsyslog:logrotate - Add a configuration snippet for logrotate
app-admin/rsyslog:relp - Add support for the Reliable Event Logging Protocol using dev-libs/librelp
app-admin/sshguard:ipfilter - Enable ipfilter firewall support (only for *bsd)
app-admin/syslog-ng:spoof-source - Enable support for spoofed source addresses
app-admin/syslog-ng:sql - Enable support for SQL destinations
app-admin/sysstat:cron - Install /etc/cron.d script to periodically run sar
app-admin/sysstat:isag - Install isag, the Interactive System Activity Graph tool
app-admin/testdisk:ntfs - Include the ability to read NTFS filesystems
app-admin/testdisk:reiserfs - include reiserfs reading ability
app-admin/ulogd:mysql - Build MYSQL output plugin to save packets in a mysql database.
app-admin/ulogd:pcap - Build PCAP output plugin to save packets in PCAP format. Uses the net-libs/libpcap library
app-admin/ulogd:postgres - Build PGSQL output plugin to save packets in a postgres database.
app-admin/ulogd:sqlite - Build SQLITE3 output plugin to save packets in an sqlite database.
app-admin/webalizer:xtended - Include the 404 extension
app-antivirus/clamav:clamdtop - A Top like tool which shows what clamd is currently scanning amongst other things
app-arch/cabextract:extra-tools - Install experimental tools: wince_info and wince_rename for examining and processing Windows CE installation cabinet header files; cabinfo for examining the structure of a cab file.
app-arch/cfv:bittorrent - Enable support for checking .torrent files
app-arch/dpkg:dselect - Build the dselect package-management frontend
app-arch/dump:ermt - encrypted rmt support
app-arch/file-roller:nautilus - Enable file-roller to integrate with gnome-base/nautilus by providing entries in its context menu.
app-arch/gzip:pic - disable optimized assembly code that is not PIC friendly
app-arch/libarchive:bzip2 -  Allow accessing bzip2-compressed archives through libbz2 (which comes with app-arch/bzip2). This only affects libarchive's native support: bsdtar will keep using bunzip2 as a filter if that's not built-in. 
app-arch/libarchive:static -  Build bsdtar and bsdcpio as static archives, removing dependencies over the enabled compression libraries (lzma, lzmadec, libbz2, zlib). 
app-arch/libarchive:zlib -  Allow accessing gzip-compressed archives through sys-libs/zlib. This only affects libarchive's native support: bsdtar will keep using gunzip as a filter if that's not built-in. It's also needed for supporting extraction of ZIP files. 
app-arch/p7zip:rar - Enable support for non-free rar decoder
app-arch/pbzip2:symlink - Install symlinks which override app-arch/bzip2 implementation
app-arch/rpm:magic - Add magic file support (sys-apps/file)
app-arch/rpm:webdav-neon - Include support for net-libs/neon
app-arch/squeeze:pathbar - Include pathbar feature
app-arch/squeeze:toolbar - Include toolbar feature
app-backup/amanda:devpay - Support for using Amazon DevPay with S3
app-backup/amanda:s3 - Support for backing up to the Amazon S3 system
app-backup/amanda:xfs - Support for backing up raw XFS filesystems using xfsdump
app-backup/backup-manager:s3 - Support for backing up to the Amazon S3 system
app-backup/bacula:bacula-clientonly - Disable DB support, and just build a client
app-backup/bacula:bacula-nodir - Disable building of director
app-backup/bacula:bacula-nosd - Disable building of storage daemon
app-backup/bacula:logwatch - Install support files for logwatch
app-backup/boxbackup:client-only - Disable server support, and just build a client
app-backup/dar:dar32 - Enables --enable-mode=32 option, which replace infinite by 32 bit integers
app-backup/dar:dar64 - Enables --enable-mode=64 option, which replace infinite by 64 bit integers
app-backup/duplicity:s3 - Support for backing up to the Amazon S3 system
app-backup/tsm:hsm - Installs Tivoli Storage Manager for Space Management
app-benchmarks/bootchart:acct - Enable process accounting
app-benchmarks/jmeter:beanshell - Enable BeanShell scripting support
app-cdr/backlite:mplayer - Add support for mplayer preview in addition to X11 and phonon
app-cdr/brasero:beagle - Enable app-misc/beagle support for searches
app-cdr/brasero:introspection - Use dev-libs/gobject-introspection for introspection
app-cdr/brasero:libburn - Enable dev-libs/libburn backend
app-cdr/brasero:nautilus -  Build gnome-base/nautilus extension
app-cdr/brasero:playlist - Enable support for playlists through dev-libs/totem-pl-parser
app-cdr/cdemu:cdemud - Pull app-cdr/cdemud dependency, useful in chroot environment (bug #315491). Do not disable until you know what you are doing.
app-cdr/cdrdao:gcdmaster - Enable building of gcdmaster application
app-cdr/cdrdao:pccts - Use dev-util/pccts instead of the built-in substitution
app-cdr/cdrkit:hfs - Provide building of HFS (Apple) CD-images
app-cdr/disc-cover:cdrom - Enable audio CD support. This is not needed to make www-apps/disc-cover work.
app-cdr/k3b:emovix - Enable burning support for eMoviX images
app-cdr/k3b:wav - Enable support for reading WAVE files
app-cdr/mybashburn:normalize - Add support for normalizing audio file volume levels
app-cdr/serpentine:muine - Enable support for the GNOME music player Muine
app-cdr/xfburn:thunar - Use Thunar VFS layer for mimetype and icons support (WARNING: deprecated, will be replaced by GIO in future)
app-crypt/ccid:twinserial - Enable twinserial reader
app-crypt/ekeyd:usb -  Build the libusb-based userland daemon for accessing the EntropyKey (alternative to the CDC USB driver). It is suggested to use this option by default, as the CDC driver in the kernel often seems to be fragile (or the gadget implementation on the EntropyKey is too buggy), and can cause various problems. 
app-crypt/gnupg:idea - Use the patented IDEA algorithm
app-crypt/gnupg:openct - build using dev-libs/openct compat
app-crypt/gnupg:pcsc-lite - build with sys-apps/pcsc-lite
app-crypt/gpgme:common-lisp - Install common-lisp files
app-crypt/gpgme:pth - Enable support for GNU Portable Threads multithreading library
app-crypt/heimdal:X -  Building X applications 
app-crypt/heimdal:berkdb -  Berkeley DB is preferred before NDBM, but if you for some reason want to use NDBM instead, you can disable this USE flag. 
app-crypt/heimdal:hdb-ldap -  Enable support for LDAP as database backend (not suggested to use) 
app-crypt/heimdal:ipv6 -  Enable/Disable ipv6 support. No magic here. 
app-crypt/heimdal:otp -  Enable support for one-time passwords (OTP) in some heimdal apps 
app-crypt/heimdal:pkinit -  Enable pkinit support to get the initial ticket 
app-crypt/heimdal:ssl -  Enable usage of openssl 
app-crypt/heimdal:threads -  Enable pthread support 
app-crypt/kstart:afs -  Enables afs support which means you can acquire an afs token and set PAGs. It's recommended to set this USE if you need authenticated access to an AFS cell for your daemon/app. 
app-crypt/mit-krb5:doc -  Creates and installs the API and implementation documentation. This is only useful if you want to develop software which depends on kerberos. 
app-crypt/mit-krb5:pkinit - Enable pkinit support for the initial ticket.
app-crypt/ophcrack-tables:vistafree - Installs the free Vista ophcrack tables
app-crypt/ophcrack-tables:xpfast - Installs the fast XP ophcrack tables
app-crypt/ophcrack-tables:xpsmall - Installs the small free XP ophcrack tables
app-crypt/seahorse:introspection - Use dev-libs/gobject-introspection for introspection
app-crypt/seahorse:ldap - Enable seahorse to manipulate GPG keys on a LDAP server.
app-crypt/seahorse-plugins:applet - Enable seahorse applet for gnome-base/gnome-panel
app-crypt/seahorse-plugins:gedit - Enable text encryption plugin to integrate into app-editors/gedit
app-crypt/seahorse-plugins:nautilus - Enable file encryption plugin to integrate into the gnome-base/nautilus context menu
app-dicts/aspell-be:classic - Support classic spelling by default
app-doc/doxygen:nodot - removes graphviz dependency, along with dot graphs
app-doc/doxygen:tcl - adds experimental support for parsing/documenting Tcl source code
app-doc/heirloom-doctools:cxx -  Build the mpm utility; this is disabled by default because it's rarely used and the only C++ tool in the suite. 
app-doc/linuxfromscratch:htmlsingle - Also install all-in-one-page HTML version
app-doc/pms:html - Generate PMS as .html as well
app-doc/tldp-howto:html - Install the docs in multipage HTML format (default)
app-doc/tldp-howto:htmlsingle - Install the docs in single page HTML format
app-doc/tldp-howto:pdf - Install the docs in pdf format
app-doc/tldp-howto:text - Install the docs in plain text format
app-editors/bluefish:gucharmap - Enable gucharmap dictionary plugin
app-editors/cssed:plugins - Install plugin development files
app-editors/emacs:gconf - Use gnome-base/gconf to read the system font name
app-editors/emacs:gzip-el - Compress bundled Emacs Lisp source
app-editors/emacs:hesiod - Enable support for net-dns/hesiod
app-editors/emacs:leim - Add support for Emacs input methods
app-editors/emacs:sendmail - Build Emacs with MTA support
app-editors/emacs:sound - Enable sound
app-editors/emacs:toolkit-scroll-bars - Use the selected toolkit's scrollbars in preference to Emacs' own scrollbars
app-editors/emacs-vcs:gconf - Use gnome-base/gconf to read the system font name
app-editors/emacs-vcs:gzip-el - Compress bundled Emacs Lisp source
app-editors/emacs-vcs:hesiod - Enable support for net-dns/hesiod
app-editors/emacs-vcs:imagemagick - Use media-gfx/imagemagick for image processing
app-editors/emacs-vcs:libxml2 - Use dev-libs/libxml2 to parse XML instead of the internal Lisp implementations
app-editors/emacs-vcs:sound - Enable sound
app-editors/emacs-vcs:toolkit-scroll-bars - Use the selected toolkit's scrollbars in preference to Emacs' own scrollbars
app-editors/fe:sendmail - Send mail after editor abend
app-editors/gedit-plugins:bookmarks - Advanced Bookmarking, it remembers all the bookmarks you ever toggled, highlights them in the text and allows you to navigate through a list with the navigation pane
app-editors/gedit-plugins:bracketcompletion - Automatically adds closing brackets
app-editors/gedit-plugins:charmap -  Insert special characters just by clicking on them
app-editors/gedit-plugins:colorpicker - Pick a color from a dialog and insert its hexadecimal representation
app-editors/gedit-plugins:drawspaces - Draw spaces and tabs
app-editors/gedit-plugins:joinlines - Join several lines or split long ones
app-editors/gedit-plugins:showtabbar - Add a menu entry to show/hide the tabbar
app-editors/gedit-plugins:smartspaces - Forget you're not using tabulations
app-editors/gedit-plugins:terminal - Embed a terminal in the bottom pane
app-editors/gvim:netbeans - Include netbeans externaleditor integration support
app-editors/gvim:nextaw - Include support for the neXtaw GUI
app-editors/jasspa-microemacs:nanoemacs - Build NanoEmacs instead of MicroEmacs
app-editors/joe:xterm - Enable full xterm clipboard support
app-editors/leafpad:emacs - Enable Emacs key theme
app-editors/nano:debug -  Enable debug messages and assert warnings. Note that these will all be sent straight to stderr rather than some logging facility. 
app-editors/nano:justify - Enable justify/unjustify functions for text formatting.
app-editors/nano:minimal -  Disable all fancy features, including ones that otherwise have a dedicated USE flag (such as spelling). 
app-editors/tea:aspell - Enable spell checking using aspell
app-editors/tea:enchant - Enable spell checking using enchant
app-editors/tea:hacking - Enable hacking support
app-editors/tea:hunspell - Enable spellchecking using hunspell
app-editors/vim:X - Link console vim against X11 libraries to enable title and clipboard features in xterm
app-editors/vim:vim-pager - Install vimpager and vimmanpager links
app-editors/xemacs:athena - Chooses the MIT Athena widget set
app-editors/xemacs:dnd - Enables support for the x11-libs/dnd drag-n-drop library
app-editors/xemacs:eolconv - Support detection and translation of newline conventions
app-editors/xemacs:pop - Support POP for mail retrieval
app-editors/xemacs:xim - Enable X11 XiM input method
app-editors/xmlcopyeditor:guidexml - Install GuideXML templates to work with Gentoo official docs
app-editors/zile:valgrind - Enable usage of dev-util/valgrind in tests
app-emacs/auctex:preview-latex - Use bundled preview-latex
app-emacs/bbdb:tex - Install plain TeX support files
app-emacs/company-mode:ropemacs - Install backend for dev-python/ropemacs 
app-emacs/company-mode:semantic - Install backend for semantic (app-emacs/cedet)
app-emacs/delicious:planner - Include support for app-emacs/planner
app-emacs/easypg:gnus - Include support for the Gnus newsreader
app-emacs/emacs-common-gentoo:emacs22icons - Install Emacs 22 style icons
app-emacs/emhacks:jde - Enable support for Java Development Environment
app-emacs/org-mode:contrib - Install user-contributed files
app-emacs/remember:bbdb - Include support for app-emacs/bbdb
app-emacs/remember:planner - Include support for app-emacs/planner
app-emacs/slime:xref - Install xref.lisp cross-referencing tool
app-emacs/vm:bbdb - Include support for app-emacs/bbdb
app-emacs/wanderlust:bbdb - Include support for app-emacs/bbdb
app-emacs/wikipedia-mode:outline-magic - Enable support for outline-mode extensions (app-emacs/outline-magic)
app-emulation/basiliskII-jit:fbdev - Enables framebuffer support
app-emulation/basiliskII-jit:jit - Enables the jit compiler
app-emulation/bochs:debugger - Enable the bochs debugger
app-emulation/e-uae:capslib - Add CAPS library support
app-emulation/e-uae:sdl-sound - Use media-libs/sdl-sound for audio output
app-emulation/fuse:libdsk - Enable support for the floppy disk emulation library app-emulation/libdsk
app-emulation/ganeti:drbd - Enable DRBD support
app-emulation/ganeti:filestorage - Enable File Storage
app-emulation/ganeti:kvm - Enable KVM support
app-emulation/ganeti:xen - Enable Xen support
app-emulation/lib765:libdsk - Enable support for the floppy disk emulation library app-emulation/libdsk
app-emulation/libvirt:iscsi -  Allow using an iSCSI remote storage server as pool for disk image storage 
app-emulation/libvirt:json -  Support QEmu 0.13 JSON-based interface, using dev-libs/yajl. 
app-emulation/libvirt:libvirtd -  Builds the libvirtd daemon as well as the client utilities instead of just the client utilities 
app-emulation/libvirt:lvm -  Allow using the Logical Volume Manager (sys-apps/lvm2) as pool for disk image storage 
app-emulation/libvirt:lxc -  Support management of Linux Containers virtualisation (app-emulation/lxc) 
app-emulation/libvirt:macvtap -  Support for MAC-based TAP (macvlan/macvtap). For networking instead of the normal TUN/TAP. It has its advantages and disadvantages. macvtap support requires very new kernels and is currently evolving. Support for this is experimental at best 
app-emulation/libvirt:network -  Enable networking support for guests 
app-emulation/libvirt:nfs -  Allow using Network File System mounts as pool for disk image storage 
app-emulation/libvirt:numa -  Use NUMA for memory segmenting via sys-process/numactl 
app-emulation/libvirt:openvz -  Support management of OpenVZ virtualisation (see sys-kernel/openvz-sources) 
app-emulation/libvirt:parted -  Allow using real disk partitions as pool for disk image storage, using sys-block/parted to create, resize and delete them. 
app-emulation/libvirt:pcap -  Support auto learning IP addreses for routing 
app-emulation/libvirt:phyp -  Support management of virtualisation through the PHYP hypervisor protocol. 
app-emulation/libvirt:qemu -  Support management of QEmu virtualisation (one of app-emulation/qemu, app-emulation/qemu-kvm or app-emulation/qemu-spice) 
app-emulation/libvirt:uml -  Support management of User Mode Linux virtualisation 
app-emulation/libvirt:virtualbox -  Support management of VirtualBox virtualisation (one of app-emulation/virtualbox or app-emulation/virtualbox-ose) 
app-emulation/libvirt:xen -  Support management of Xen virtualisation (app-emulation/xen) 
app-emulation/lxc:vanilla -  Avoid adding Gentoo Linux-specific modifications, which include the custom init script. This is present as a flag to avoid forcing dependencies over users that might not want have them around as they use LXC in contexts where the init script is not useful. 
app-emulation/mol:oldworld - Includes Macintosh's OldWorld support
app-emulation/mol:pci - Experimental PCI proxy support
app-emulation/mol:sheep - Support for the sheep net driver
app-emulation/open-vm-tools:doc - Generate API documentation
app-emulation/open-vm-tools:fuse - Build vmblock-fuse in favor of FUSE based blocking mechanism for DnD
app-emulation/open-vm-tools:pic - Force shared libraries to be built as PIC
app-emulation/open-vm-tools:unity - Enable host unity support
app-emulation/opennebula:qemu - Pull in packages needed to create Qemu/Kvm nodes.
app-emulation/opennebula:xen - Pull in packages needed to create Xen nodes.
app-emulation/pearpc:jit - Use the JITC-x86 CPU
app-emulation/q4wine:gnome - Use the gksu sudo GUI for managing the devices
app-emulation/q4wine:icoutils -  Enable icoutils support 
app-emulation/q4wine:kde - Use the kdesu sudo GUI for managing the devices
app-emulation/q4wine:wineappdb -  Enable Win AppDB browser subsystem
app-emulation/qemu:alsa - Enable alsa output for sound emulation
app-emulation/qemu:esd - Enable esound output for sound emulation
app-emulation/qemu:gnutls - Enable TLS support for the VNC console server
app-emulation/qemu:kqemu - Enables the kernel acceleration module on a x86/x86-64 cpu
app-emulation/qemu:kvm - Use the KVM (Kernel Virtual Machine) infrastructure on compatible hardware
app-emulation/qemu:ncurses - Enable the ncurses-based console
app-emulation/qemu:pulseaudio - Enable pulseaudio output for sound emulation
app-emulation/qemu:sdl - Enable the SDL-based console
app-emulation/qemu:vde - Enable Virtual Distributed Ethernet (VDE) based networking
app-emulation/qemu-kvm:aio - Enables support for Linux's Async IO
app-emulation/qemu-kvm:alsa - Enable alsa output for sound emulation
app-emulation/qemu-kvm:brltty - Adds support for braille displays using brltty
app-emulation/qemu-kvm:esd - Enable esound output for sound emulation
app-emulation/qemu-kvm:fdt - Enables firmware device tree support
app-emulation/qemu-kvm:jpeg - Enable JPEG compression for the VNC console server
app-emulation/qemu-kvm:kvm-trace - Allows you to use KVM tracing
app-emulation/qemu-kvm:ncurses - Enable the ncurses-based console
app-emulation/qemu-kvm:png - Enable PNG compression for the VNC console server
app-emulation/qemu-kvm:pulseaudio - Enable pulseaudio output for sound emulation
app-emulation/qemu-kvm:qemu-ifup - Provides the qemu-ifup script for use with QEMU's built in bridging
app-emulation/qemu-kvm:sdl - Enable the SDL-based console
app-emulation/qemu-kvm:ssl - Enable TLS support for the VNC console server
app-emulation/qemu-kvm:vde - Enable VDE-based networking
app-emulation/qemu-kvm:xen - Enables support for Xen backends
app-emulation/qemu-kvm-spice:aio - Enables support for Linux's Async IO
app-emulation/qemu-kvm-spice:alsa - Enable alsa output for sound emulation
app-emulation/qemu-kvm-spice:esd - Enable esound output for sound emulation
app-emulation/qemu-kvm-spice:fdt - Enables firmware device tree support
app-emulation/qemu-kvm-spice:gnutls - Enable TLS support for the VNC console server
app-emulation/qemu-kvm-spice:kvm-trace - Allows you to use KVM tracing
app-emulation/qemu-kvm-spice:ncurses - Enable the ncurses-based console
app-emulation/qemu-kvm-spice:pulseaudio - Enable pulseaudio output for sound emulation
app-emulation/qemu-kvm-spice:qemu-ifup - Provides the qemu-ifup script for use with QEMU's built in bridging
app-emulation/qemu-kvm-spice:sdl - Enable the SDL-based console
app-emulation/qemu-kvm-spice:vde - Enable VDE-based networking
app-emulation/qemu-softmmu:alsa - Enable alsa output for sound emulation
app-emulation/qemu-softmmu:gnutls - Enable TLS support for the VNC console server
app-emulation/qemu-softmmu:kqemu - Enables the kernel acceleration module on a x86/x86-64 cpu
app-emulation/qemu-softmmu:sdl - Enable the SDL-based console
app-emulation/spice:gui - Build some GUI components (inside the guest window).
app-emulation/uae:scsi - Enable the uaescsi.device
app-emulation/uae:sdl-sound - Use media-sound/sdl-sound for audio output
app-emulation/uae:ui - Build the user interface (could be gtk or ncurses based, depending on sdl, dga, svga and aalib USE flags)
app-emulation/vice:ethernet - Enable ethernet emulation
app-emulation/vice:memmap - Enable extra monitor features
app-emulation/vice:xrandr - Enable support for the X xrandr extension
app-emulation/virt-manager:policykit -  Enables sys-auth/polkit authentication support, required when using app-emulation/libvirt with PolicyKit authentication 
app-emulation/virt-manager:sasl -  Depend on the proper libraries needed to connect to SASL-enabled libvirtd instances (e.g. Kerberos-protected instances). 
app-emulation/virtualbox-bin:additions - Install Guest System Tools ISO
app-emulation/virtualbox-bin:chm - Install kchmviewer binary to enable online help (in MS CHM format)
app-emulation/virtualbox-bin:headless - Install without any graphic frontend
app-emulation/virtualbox-bin:rdesktop-vrdp - Install the rdesktop client integration
app-emulation/virtualbox-bin:sdk - Enable building of SDK
app-emulation/virtualbox-bin:vboxwebsrv - Install the VirtualBox webservice
app-emulation/virtualbox-ose:additions - Install Guest System Tools ISO
app-emulation/virtualbox-ose:headless - Build without any graphic frontend
app-emulation/virtualbox-ose:sdk - Enable building of SDK
app-emulation/virtualbox-ose:vboxwebsrv - Build and install the VirtualBox webservice
app-emulation/vov:gprof - build with profiling support
app-emulation/wine:capi - Enable ISDN support via CAPI
app-emulation/wine:custom-cflags - Bypass strip-flags; use are your own peril
app-emulation/wine:gecko - Add support for the Gecko engine when using iexplore
app-emulation/wine:perl - Install helpers written in perl (winedump/winemaker)
app-emulation/wine:samba - Add support for NTLM auth. see http://wiki.winehq.org/NtlmAuthSetupGuide and http://wiki.winehq.org/NtlmSigningAndSealing
app-emulation/wine:win32 - Build a 32bit version of Wine (won't run Win64 binaries)
app-emulation/wine:win64 - Build a 64bit version of Wine (won't run Win32 binaries)
app-emulation/xen:acm - Enable the ACM/sHype XSM module from IBM
app-emulation/xen:flask - Enable the Flask XSM module from NSA
app-emulation/xen:pae - Enable support for PAE kernels (usually x86-32 with >4GB memory)
app-emulation/xen:xsm - Enable the Xen Security Modules (XSM)
app-emulation/xen-tools:acm - Enable the ACM/sHype XSM module from IBM
app-emulation/xen-tools:api - Build the C libxenapi bindings
app-emulation/xen-tools:flask - Enable the Flask XSM module from NSA
app-emulation/xen-tools:hvm - Enable support for hardware based virtualization (VT-x, AMD-v
app-emulation/xen-tools:ioemu - Enable IOEMU support
app-emulation/xen-tools:pygrub - Install the pygrub boot loader
app-emulation/xen-tools:screen - Enable support for running domain U console in an app-misc/screen session
app-forensics/afflib:ewf - Enable libewf extra formats
app-forensics/afflib:fuse - Enable extra fuse thingies
app-forensics/afflib:qemu - Enable qemu stuff
app-forensics/afflib:s3 - Enable S3
app-forensics/aide:audit - Enable support for sys-process/audit
app-forensics/aide:prelink - Enable support for sys-devel/prelink
app-forensics/libewf:rawio - Enables raw IO handling
app-forensics/openscap:nss - Prefer NSS over libgcrypt as the crypto engine
app-forensics/rdd:rawio - Enables raw IO handling
app-forensics/sleuthkit:aff - Enable extra aff formats
app-forensics/sleuthkit:dbtool - Add patch for dbtool interface from PyFlag
app-forensics/sleuthkit:ewf - Enable libewf support
app-i18n/fcitx:pango - Enable support for x11-libs/pango
app-i18n/ibus:gconf - Enable support for gnome-base/gconf
app-i18n/ibus:introspection - Use dev-libs/gobject-introspection for introspection
app-i18n/ibus:vala - Enable support for dev-lang/vala
app-i18n/ibus-mozc:ibus - Enable support for app-i18n/ibus
app-i18n/ibus-mozc:scim - Enable support for app-i18n/scim
app-i18n/ibus-table-xingma:extra-phrases - Add extra phrases into builded Engine
app-i18n/im-ja:anthy - Support for Anthy input method
app-i18n/im-ja:skk - Support for SKK input method
app-i18n/kimera:anthy - Support for Anthy input method
app-i18n/libtomoe-gtk:gucharmap - Enable gucharmap dictionary plugin
app-i18n/scim-tomoe:gucharmap - Enable gucharmap dictionary plugin
app-i18n/sunpinyin:ibus - Enable support for app-i18n/ibus input method 
app-i18n/sunpinyin:xim - Enable support for XIM
app-i18n/tomoe:hyperestraier - Enable support for app-text/hyperestraier
app-i18n/uim:anthy - Enable support for app-i18n/anthy input method 
app-i18n/uim:eb - Enable support for dev-libs/eb
app-i18n/uim:ffi - Enable support for virtual/libffi
app-i18n/uim:prime - Enable support for app-i18n/prime
app-i18n/uim:skk - Enable support for app-i18n/skk-jisyo
app-laptop/ibam:gkrellm - Enable building of app-admin/gkrellm module
app-laptop/laptop-mode-tools:scsi - Adds dependency on sdparm to control non-SATA SCSI drivers
app-laptop/pbbuttonsd:ibam - Enable support for Intelligent Battery Monitoring
app-laptop/pbbuttonsd:macbook - Enable support for the Macbook and Macbook Pro
app-laptop/tp_smapi:hdaps - Install a compatible HDAPS module
app-laptop/tpctl:tpctlir - Enable support for thinkpad models 760 and 765
app-misc/anki:furigana -  Enable support for furigana generation 
app-misc/anki:graph -  Enable support for making graphs 
app-misc/anki:recording -  Enable support for audio recording 
app-misc/anki:sound -  Enable support for adding sound to cards 
app-misc/beagle:chm - Enables support for indexing of the MS CHM (Compressed HTML) file format using app-doc/chmlib.
app-misc/beagle:debug - Enables debug XML dumps of all messages passed between the daemons and the UIs. WARNING, this option will fill up your Beagle Log directory very quickly.
app-misc/beagle:doc - Builds programmer documentation for Beagle using app-doc/monodoc.
app-misc/beagle:eds - Enables Beagle to index the Addressbook and Calendar from mail-client/evolution stored in gnome-extra/evolution-data-server. The information is accessed using dev-dotnet/evolution-sharp.
app-misc/beagle:firefox - Compiles and installs the extension for either www-client/firefox or www-client/firefox-bin. This extension helps Beagle index the websites you visit.
app-misc/beagle:galago - Allows Beagle to get status information from applications such as Pidgin to show in the search results.
app-misc/beagle:google - Enables google (gmail etc.) indexing support.
app-misc/beagle:gtk - Enables the GTK+ Beagle Search UI for showing search results. This is the default GUI for Beagle.
app-misc/beagle:inotify - Enable inotify filesystem monitoring support 
app-misc/beagle:ole - Enables OLE (Object Linking and Editing) support via dev-dotnet/gsf-sharp, app-text/wv, and app-office/gnumeric(ssindex). These allow Beagle to index MS Powerpoint, Word, and Spreadsheet Documents.
app-misc/beagle:pdf - Enables support for indexing of the PDF (Portable Document Format) file format using `pdfinfo` and `pdftotext` from app-text/poppler
app-misc/beagle:thunderbird - Compiles and installs the extension for either mail-client/thunderbird or mail-client/thunderbird-bin. This extension helps Beagle index your mails.
app-misc/beagle:xscreensaver - Allow Beagle to detect when the screensaver is switched on. This allows Beagle to use more resources and index faster when the computer is not in use.
app-misc/digitemp:ds2490 - Build support for the ds2490 sensor
app-misc/digitemp:ds9097 - Build support for the ds9097 sensor
app-misc/digitemp:ds9097u - Build support for the ds9097u sensor
app-misc/fdupes:md5sum-external - Use external md5sum program instead of bundled md5sum routines
app-misc/freemind:groovy - Build plugin for scripting via Groovy
app-misc/freemind:latex - Build plugin for inserting mathematical formulas in LaTeX syntax
app-misc/freemind:pdf - Build plugin for exporting mindmaps to SVG and PDF
app-misc/freemind:svg - Build plugin for exporting mindmaps to SVG and PDF
app-misc/geneweb:ocamlopt - Enable ocamlopt support (dev-lang/ocaml native code compiler)
app-misc/gnote:applet - Enable gnote applet for gnome-base/gnome-panel
app-misc/gourmet:gnome-print - Enable pretty Python printing with gnome-print
app-misc/gourmet:rtf - Enable export to RTF
app-misc/gpsdrive:garmin - Adds specific support for Garmin GPS receivers (pre-2.10 only)
app-misc/gpsdrive:gdal - Include gdal and ogr support for format conversions.
app-misc/gpsdrive:kismet - Include support for kismet wifi mapping.
app-misc/gpsdrive:mapnik - Include mapnik support for custom map creation.
app-misc/gpsdrive:scripts - Include some of the additional helper scripts.
app-misc/gpsdrive:speech - Include speech support.
app-misc/gramps:mozembed - Use Mozilla-based rendering for geographical data view.
app-misc/gramps:reports - All external software that is needed for graphical reports will be installed
app-misc/gramps:webkit - Use Webkit-based rendering for geographical data view.
app-misc/graphlcd-base:g15 - Add support for app-misc/g15daemon driver (e.g. Logitech G15 Keybord)
app-misc/lcd-stuff:mpd - Add support for display of mpd controlled music (media-libs/libmpd)
app-misc/lcd4linux:mpd - Add support for display of mpd controlled music (media-libs/libmpd)
app-misc/lcdproc:ftdi - Enable support for FTDI connections in some selected LCD_DEVICES (currently hd44780)
app-misc/lcdproc:irman - Enable support for IRMan (media-libs/libirman)
app-misc/lcdproc:nfs - Adds support for NFS file system
app-misc/lcdproc:seamless-hbars - Try to avoid gaps in horizontal bars
app-misc/lirc:hardware-carrier - The transmitter device generates its clock signal in hardware
app-misc/lirc:transmitter - Add transmitter support to some lirc-drivers (e.g. serial)
app-misc/mc:edit - Build mcedit application
app-misc/note:general - Add support for ascii flatfile backend
app-misc/note:text - Add support for text backend
app-misc/roadnav:festival - Enable support for app-accessibility/festival
app-misc/roadnav:flite - Enable support for app-accessibility/flite (festival-lite)
app-misc/roadnav:openstreetmap - Enable openstreetmap support
app-misc/roadnav:scripting - Enable scripting support
app-misc/screen:multiuser - Enable multiuser support (by setting correct permissions)
app-misc/screen:nethack - Express error messages in nethack style
app-misc/sphinx:id64 - use 64-bit document and word IDs
app-misc/sphinx:stemmer - Enable language stemming support
app-misc/strigi:clucene - Enable dev-cpp/clucene backend support.
app-misc/strigi:hyperestraier - Enable app-text/hyperestraier backend support.
app-misc/strigi:inotify - Enable support for inotify.
app-misc/strigi:log - Enables advanced logging through dev-libs/log4cxx.
app-misc/tablix:pvm - Add support for parallel virtual machine (sys-cluster/pvm)
app-misc/tasque:hiveminder -  Allows you to use http://www.hiveminder.com/ as your storage backend. 
app-misc/tasque:rememberthemilk -  Allows you to use http://www.rememberthemilk.com/ as your storage backend. 
app-misc/tomboy:applet - Enable tomboy applet for gnome-base/gnome-panel
app-misc/tomboy:galago - Add support for the galago desktop presence framework (dev-dotnet/galago-sharp)
app-misc/towitoko:moneyplex - Makes libtowitoko work for the moneyplex home banking software
app-misc/tracker:applet - Build tracker monitor applet
app-misc/tracker:gsf - Enable gnome-extra/libgsf based data extractor and for ODT.
app-misc/tracker:iptc - Enable extraction of IPTC data from pictures
app-misc/tracker:kmail - Build kmail data miner
app-misc/tracker:laptop - Make tracker power management aware
app-misc/tracker:nautilus - Enable tracker to integrate with gnome-base/nautilus by providing entries in its context menu 
app-misc/tracker:playlist - Add support for playlists
app-misc/tracker:strigi - Add support for app-misc/strigi search engine.
app-misc/tracker:upnp - Add support for video extraction via media-libs/gupnp-dlna.
app-misc/worker:avfs - Enable support for sys-fs/avfs
app-misc/workrave:distribution - Enable networking. See http://www.workrave.org/features/
app-mobilephone/gammu:irda - Enables infrared support
app-mobilephone/gnokii:ical - Enable support for dev-libs/libical
app-mobilephone/gnokii:irda - Enable infrared support
app-mobilephone/gnokii:sms - Enable SMS support (build smsd)
app-mobilephone/obexd:nokia - Add support for Nokia backup plugin
app-mobilephone/obexd:server - Enables server installation, it's incompatible with obex-data-server provided one
app-mobilephone/obexftp:swig - Enable rebuild of dev-lang/swig bindings
app-mobilephone/smstools:stats - Enable statistic reporting
app-mobilephone/yaps:capi - Enable CAPI support
app-office/abiword:collab - Enable collaborative editing plugin
app-office/abiword:grammar - Enable grammar checking via dev-libs/link-grammar
app-office/abiword:math - Enable support for x11-libs/gtkmathview
app-office/abiword:openxml - Enable OpenXML support
app-office/abiword:ots - Enable Text Summarizer plugin
app-office/abiword:plugins - Enable plugins build
app-office/abiword:thesaurus - Enable thesaurus support
app-office/abiword:wordperfect - Enable wordperfect file support via app-text/libwpd
app-office/abiword-plugins:grammar - Enable grammar checking via dev-libs/link-grammar
app-office/abiword-plugins:math - Enable support for x11-libs/gtkmathview
app-office/abiword-plugins:ots - Enable Text Summarizer plugin
app-office/abiword-plugins:thesaurus - Enable thesaurus support
app-office/abiword-plugins:wordperfect - Enable wordperfect file support via app-text/libwpd
app-office/akonadi-server:server - Use locally installed database server.
app-office/glabels:barcode - Enable barcode support through external libraries.
app-office/gnucash:chipcard - Enable support for chipcard reading and processing.
app-office/gnucash:hbci - Enable HBCI support, for connecting to some internet banks
app-office/gnucash:quotes - Enable Online Stock Quote retrieval
app-office/gnucash:webkit - Use net-libs/webkit-gtk for rendering rather than gnome-extra/gtkhtml
app-office/gnumeric:gnome - Allow Gnumeric to use GNOME specific extensions.
app-office/gnumeric:perl - Enable perl plugin loader.
app-office/gnumeric:python - Enable python plugin loader.
app-office/grisbi:print - Enable printing support
app-office/imposter:iksemel - Enable external dev-libs/iksemel parsing support
app-office/karbon:pstoedit - Build support for PDF and PS import.
app-office/karbon:wpg - Build wordperfect image support.
app-office/kchart:reports - Enable the reports koffice module in kchart, also used by kplato and kexi
app-office/kexi:reports - Enable the reports koffice module in kchart, also used by kplato and kexi
app-office/kexi:xbase - Build support for xbase db types.
app-office/kmymoney:hbci - Enable HBCI support using net-libs/aqbanking
app-office/kmymoney:quotes - Enable Online Stock Quote retrieval
app-office/koffice-libs:reports - Enable the reports koffice module in kchart, also used by kplato and kexi
app-office/koffice-meta:reports - Enable the reports koffice module in kchart, also used by kplato and kexi
app-office/krita:gmm - Enable library for sparse, dense and skyline matrices.
app-office/krita:kdcraw - Enable KDE image manipulating interface.
app-office/kspread:solver - Use solver extension for solving lingebra and others.
app-office/kword:wpd - Build wordperfect document support.
app-office/kword:wv2 - Build MS-Word .doc support.
app-office/lyx:dia - Add support for diagrams (app-office/dia)
app-office/lyx:docbook - Add support for docbook export
app-office/lyx:dot - Add support for DOT import (media-gfx/graphviz) 
app-office/lyx:html - Add support for HTML import
app-office/lyx:monolithic-build - This should speed up compilation significantly when you have enough RAM (> 600 MB)
app-office/lyx:rcs - Add support for revision control via dev-vcs/rcs 
app-office/lyx:rtf - Add support for RTF import/export packages
app-office/openoffice:binfilter - Enable support for legacy StarOffice 5.x and earlier file formats
app-office/openoffice:odk - Build the Office Development Kit
app-office/openoffice:templates - Enable installation of Sun templates
app-office/rabbit:gnome-print - Gnome-Print support (gnome-base/libgnomeprint)
app-office/rabbit:gs - Ghostscript support (app-text/ghostscript-gpl)
app-office/rabbit:tgif - tgif support (media-gfx/tgif)
app-office/scribus:minimal - Don't install headers (only required for e.g. plug-in developers)
app-office/texmacs:netpbm - Add support for media-libs/netpbm
app-office/tpp:figlet - Install app-misc/figlet to support the --huge command
app-pda/barry:boost - Enable boost support
app-pda/barry:gui - Gui backup tool support
app-pda/barry:opensync - Enabling opensync plugin
app-pda/libopensync-plugin-irmc:irda - Enable IrDA support
app-pda/libopensync-plugin-syncml:http - Enable http transports
app-pda/libopensync-plugin-syncml:obex - Enable obex transports
app-pda/libsyncml:http - Enable http transports
app-pda/libsyncml:obex - Enable obex transports
app-pda/synce:serial - Enable serial port support (installs app-pda/synce-serial)
app-pda/synce-fur:void-chmod - enable a fake fuse hook for "chmod" that just returns 0
app-portage/conf-update:colordiff - Use colors when displaying diffs (app-misc/colordiff)
app-portage/eix:bzip2 - Support for parsing of environment.bz2 to guess repository name of packages installed with ancient portage versions (requires app-arch/bzip2). This flag is safe to disable for portage users that have re-merged all packages since 2007. This flag will be phased out.
app-portage/eix:debug - Build with CXXFLAGS/LDFLAGS for debugging support; not recommended for normal use.
app-portage/eix:deprecated - Installs wrapper scripts for all the previous executable names that will soon be going away. Enabled by default in 0.17.0, optional in 0.18.0, removed in next major release.
app-portage/eix:doc - Create description of the eix cache file additionally in html format
app-portage/eix:hardened - Add CXXFLAGS/LDFLAGS enhancing security at the cost of a slight speed loss. If a hardened gcc is used, these flags should not make a difference.
app-portage/eix:nls - Support foreign language messages (experimental; currently only de)
app-portage/eix:optimization - Adds several supplemental CXXFLAGS/LDFLAGS for optimization that upstream endorses. Absense of this USE flag does not strip user's *FLAGS
app-portage/eix:sqlite - Compile in support for portage's sqlite backend; to actually use it you need additional configuration of portage and eix
app-portage/eix:strong-optimization - Adds several more agressive CXXFLAGS/LDFLAGS for optimization like graphite (if available). May cause trouble with some buggy compiler versions. Absense of this USE flag does not strip user's *FLAGS
app-portage/eix:tools - Create separate binary for script helper tools (currently only: versionsort); useful if they are called extremely often
app-portage/gatt:libpaludis - Do some dependency resolution by using a sys-apps/paludis interface
app-portage/layman:bazaar - Support dev-vcs/bzr based overlays
app-portage/layman:darcs - Support dev-vcs/darcs based overlays
app-portage/layman:git - Support dev-vcs/git based overlays
app-portage/layman:mercurial - Support dev-vcs/mercurial based overlays
app-portage/pfl:network-cron - Adds a cron job which does a weekly submit of the package database
app-portage/portato:eix - Enable eix support
app-portage/portato:userpriv - Allow emerge processes as normal user
app-portage/tatt:templates - Install template scripts to be used with tatt
app-shells/bash:bashlogger - Log ALL commands typed into bash; should ONLY be used in restricted environments such as honeypots
app-shells/bash:mem-scramble - Build with custom malloc/free overwriting allocated/freed memory
app-shells/bash:net - Enable /dev/tcp/host/port redirection
app-shells/bash:plugins - Add support for loading builtins at runtime via 'enable'
app-shells/pdsh:rsh - This allows the use of rsh (remote shell) and rcp (remote copy) for authoring websites. sftp is a much more secure protocol and is preferred.
app-shells/scsh-install-lib:scsh - Use a non-FHS directory layout
app-shells/shish:diet - Use dev-libs/dietlibc
app-shells/tcsh:catalogs - Add support for NLS catalogs
app-text/cb2bib:poll - use clipboard polling
app-text/crm114:mew - Add support for using the mewdecode mime decoder (app-emacs/mew)
app-text/crm114:mimencode - Add support for using the mimencode mime (net-mail/metamail)
app-text/crm114:normalizemime - Add support for using the normalizemime (mail-filter/normalizemime)
app-text/cuneiform:imagemagick - Enables support of various input formats using media-gfx/imagemagick. Otherwise only uncompressed BMP files are supported. 
app-text/dictd:judy - Build Judy-based (dev-libs/judy) plugin implementing fast "exact" and especially "lev" strategies
app-text/dictd:minimal - Don't build server but dict client, dictzip and dictfmt only.
app-text/docbook-sgml-utils:jadetex - Add support for app-text/jadetex (for processing tex files produced by the TeX backend of Jade)
app-text/dvipng:t1lib - Enable support for T1lib font rendering (media-libs/t1lib)
app-text/enchant:aspell - Adds support for app-text/aspell spell checker
app-text/enchant:hunspell - Adds support for app-text/hunspell spell checker
app-text/enchant:zemberek - Adds support for app-text/zemberek-server spell checker server
app-text/evince:dvi - Enable the built-in DVI viewer
app-text/evince:gnome - Enable the use of gnome-base/gconf to honour lockdown settings
app-text/evince:introspection - Use dev-libs/gobject-introspection for introspection
app-text/evince:nautilus - Enable property page extension in gnome-base/nautilus
app-text/evince:t1lib - Enable the Type-1 fonts for the built-in DVI viewer (media-libs/t1lib)
app-text/gtranslator:http - Enable support for open translation plugin using net-libs/libsoup
app-text/hyperestraier:mecab - Enable app-text/mecab support for Estraier
app-text/lcdf-typetools:kpathsea - Enable integration with kpathsea search library (TeX related)
app-text/lodgeit:vim -  Install a vim plugin allowing to paste and download from within vim 
app-text/namazu:kakasi - Enable kakasi support (dev-perl/Text-Kakasi)
app-text/pdf2djvu:graphicsmagick - Enable media-gfx/graphicsmagick support
app-text/pdftk:nodrm - Decrypt a document with the user_pw even if it has an owner_pw set
app-text/podofo:boost - Add support for boost
app-text/poppler:abiword -  Enable support for app-office/abiword output. Requires dev-libs/libxml2. 
app-text/poppler:exceptions - Enable exceptions throwing.
app-text/poppler:utils -  Install command-line PDF converters and various utilities. 
app-text/poppler:xpdf-headers - Install xpdf headers.
app-text/sgmltools-lite:jadetex - Add support for app-text/jadetex (for processing tex files produced by the TeX backend of Jade)
app-text/stardict:espeak - Enable text to speech synthesizer using espeak engine
app-text/stardict:festival - Enable text to speech synthesizer using festival engine
app-text/stardict:gucharmap - Enable gucharmap dictionary plugin
app-text/stardict:pronounce - Install WyabdcRealPeopleTTS package (it is just many .wav files) to make StarDict pronounce English words
app-text/stardict:qqwry - Enable QQWry plugin, which provides information (in Chinese language) about geographical positions, owner, etc. for IP addresses
app-text/sword:lucene - Enable lucene support for faster searching (dev-cpp/clucene)
app-text/texlive:context - Add support for the ConTeXt format (dev-texlive/texlive-context)
app-text/texlive:cyrillic - Add support for Cyrillic (dev-texlive/texlive-langcyrillic)
app-text/texlive:detex - Add support for dev-tex/detex, a filter program that removes the LaTeX (or TeX) control sequences
app-text/texlive:dvi2tty - Add support for dev-tex/dvi2tty to preview dvi-files on text-only devices
app-text/texlive:dvipdfm - Add support for app-text/dvipdfm to convert DVI files to PDF
app-text/texlive:extra - Add support for extra TeXLive packages
app-text/texlive:games - Add typesetting support for games (chess, etc.) (dev-texlive/texlive-games)
app-text/texlive:graphics - Add support for several graphics packages (pgf, tikz,...)
app-text/texlive:humanities - Add LaTeX support for the humanities (dev-texlive/texlive-humanities)
app-text/texlive:jadetex - Add support for app-text/jadetex (for processing tex files produced by the TeX backend of Jade)
app-text/texlive:latex3 - Add support for LaTeX3 (dev-texlive/texlive-latex3)
app-text/texlive:luatex - Add extra support for luatex
app-text/texlive:music - Add support for music typesetting (dev-texlive/texlive-music)
app-text/texlive:omega - Add omega packages (dev-texlive/texlive-omega)
app-text/texlive:pstricks - Add pstricks packages (dev-texlive/texlive-pstricks)
app-text/texlive:publishers - Add support for publishers (dev-texlive/texlive-publishers)
app-text/texlive:science - Add typesetting support for natural and computer sciences (dev-texlive/texlive-science)
app-text/texlive:tex4ht - Add support for dev-tex/tex4ht (for converting (La)TeX to (X)HTML, XML and OO.org)
app-text/texlive:xetex - Add support for XeTeX macros (dev-texlive/texlive-xetex)
app-text/texlive:xindy - Add support for app-text/xindy, a flexible indexing system
app-text/texlive-core:xetex - Add support for XeTeX: a TeX system with Unicode and modern font technologies.
app-text/webgen:builder - Enable programmatic HTML/XML generation
app-text/webgen:exif - Enable EXIF information in image galleries
app-text/webgen:highlight - Enable syntax highlighting for certain plugins
app-text/webgen:markdown - Markdown support
app-text/webgen:thumbnail - Thumbnail creation support using rmagick
app-text/wklej:vim - Install the vim plugin allowing to paste through ':Wklej'.
app-text/xpdf:nodrm - Disable the drm feature decoder
app-vim/gentoo-syntax:ignore-glep31 - Remove GLEP 31 (UTF-8 file encodings) settings 
app-vim/latexsuite:html - Install HTML documentation
dev-cpp/sptk:aspell - Enable support for app-text/aspell
dev-cpp/sptk:excel - Enable Excel support
dev-cpp/xsd:ace - Enable support for serializing to/from an ACE CDR stream
dev-db/drizzle:curl -  Enable the HTTP authentication plugin (using net-misc/curl). This is needed for the tests to apply properly. 
dev-db/drizzle:doc -  Build the API documentation for the package, using app-doc/doxygen. Warning, this might take over an hour on slower machines. 
dev-db/drizzle:gearman -  Enable the gearman plugins for user-defined functions and logging (using sys-cluster/gearman). 
dev-db/drizzle:haildb -  Use the dev-db/haildb libraries to replace the innodb plugin storage engine with haildb (an innodb fork). 
dev-db/drizzle:md5 -  Enable the MD5 plugin, using dev-libs/libgcrypt; this replaces the older openssl and gnutls USE flags. 
dev-db/drizzle:memcache -  Enable the memcache plugin for user-defined functions and statistics in I_S tables (using dev-libs/libmemcached). Currently restricts tests because of an upstream testsuite bug. 
dev-db/drizzle:pam -  Enable the PAM authentication plugin (using sys-libs/pam). The configuration file created will be /etc/pam.d/drizzle. 
dev-db/drizzle:tcmalloc -  Use the dev-util/google-perftools libraries to replace the malloc() implementation with a possibly faster one. 
dev-db/firebird:client - Install client library and header files only
dev-db/firebird:superserver - Install SuperServer
dev-db/firebird:xinetd - Install ClassicServer
dev-db/haildb:debug -  Enable extra debug codepaths and assertions. If disabled, both the debug code and assertions are removed from the resulting binaries. Optimisations are untouched. 
dev-db/haildb:tcmalloc -  Use the dev-util/google-perftools libraries to replace the malloc() implementation with a possibly faster one. 
dev-db/haildb:zlib -  Add support for compressed tables through sys-libs/zlib. 
dev-db/ingres:client - Disable dbms component
dev-db/ingres:das - Enable das support
dev-db/ingres:demodb - Install demo DB
dev-db/ingres:net - Enable net support
dev-db/ingres:nodbms - Disable dbms component
dev-db/maatkit:udf - Build the MySQL UDFs shipped with maatkit, requires non-minimal MySQL
dev-db/mariadb:big-tables - Make tables contain up to 1.844E+19 rows
dev-db/mariadb:cluster - Add support for NDB clustering (deprecated)
dev-db/mariadb:community - Enables the community features from upstream.
dev-db/mariadb:embedded - Build embedded server (libmysqld)
dev-db/mariadb:extraengine - Add support for alternative storage engines (Archive, CSV, Blackhole, Federated(X), Partition)
dev-db/mariadb:latin1 - Use LATIN1 encoding instead of UTF8
dev-db/mariadb:libevent - Use libevent for connection handling
dev-db/mariadb:max-idx-128 - Raise the max index per table limit from 64 to 128
dev-db/mariadb:minimal - Install client programs only, no server
dev-db/mariadb:pbxt - Add experimental support for PBXT storage engine
dev-db/mariadb:profiling - Add support for statement profiling (requires USE=community).
dev-db/mariadb:test - Install upstream testsuites for end use.
dev-db/mysql:big-tables - Make tables contain up to 1.844E+19 rows
dev-db/mysql:cluster - Add support for NDB clustering (deprecated)
dev-db/mysql:community - Enables the community features from upstream.
dev-db/mysql:embedded - Build embedded server (libmysqld)
dev-db/mysql:extraengine - Add support for alternative storage engines (Archive, CSV, Blackhole, Federated(X), Partition)
dev-db/mysql:latin1 - Use LATIN1 encoding instead of UTF8
dev-db/mysql:max-idx-128 - Raise the max index per table limit from 64 to 128
dev-db/mysql:minimal - Install client programs only, no server
dev-db/mysql:pbxt - Add experimental support for PBXT storage engine
dev-db/mysql:profiling - Add support for statement profiling (requires USE=community).
dev-db/mysql:raid - Deprecated option, removed in the 5.0 series
dev-db/mysql:test - Install upstream testsuites for end use.
dev-db/mysql:xtradb - Add experimental support for Percona's InnoDB replacement: XtraDB
dev-db/mysql-connector-c++:gcov - Build coverage support
dev-db/postgis:geos - Add the sci-libs/geos library for exact topological tests
dev-db/postgis:proj - Add the sci-libs/proj library for reprojection features
dev-db/postgresql-base:pg-intdatetime - Enable --enable-integer-datetimes configure option, which changes PG to use 64-bit integers for timestamp storage
dev-db/postgresql-base:pg_legacytimestamp - Use double precision floating-point numbers instead of 64-bit integers for timestamp storage. 
dev-db/postgresql-server:pg_legacytimestamp - Use double precision floating-point numbers instead of 64-bit integers for timestamp storage. 
dev-db/postgresql-server:uuid - Enable server side UUID generation (via dev-libs/ossp-uuid)
dev-db/sqlite:extensions - Enable support for dynamic loading of extensions
dev-db/sqlite:fts3 - Full text search using the fts3 module
dev-db/sqlite:secure-delete - Overwrite deleted information with zeros in addition to marking the space as available for reuse. This causes a performance penalty.
dev-db/sqlite:soundex - Enable the soundex function to compute soundex encodings of strings
dev-db/sqlite:threadsafe - Enable thread safe operation of sqlite
dev-db/sqlite:unlock-notify - Adds API for notifications when a database is unlocked in shared-cache mode
dev-db/unixODBC:minimal - Disable bundled drivers and extra libraries (most users don't need these)
dev-db/unixODBC:odbcmanual - Administrator, Internal Structure, Programmer and User documentation
dev-dotnet/nant:bootstrap - Bootstrap nant by using pre-built ndoc binaries.
dev-embedded/openocd:ftd2xx - Enable support for USB FTDI chips via dev-embedded/libftd2xx
dev-embedded/openocd:ftdi - Enable support for USB FTDI chips via dev-embedded/libftdi
dev-embedded/openocd:parport - Enable support for parport JTAG devices
dev-embedded/openocd:presto - Enable support for AXIS PRESTO devices
dev-embedded/ponyprog:epiphany - Enable support for www-client/epiphany 
dev-embedded/qvfb:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia) 
dev-embedded/sdcc:boehm-gc - Enable Hans Boehm's garbage collector (dev-libs/boehm-gc)
dev-embedded/urjtag:ftdi - Enable support for USB FTDI chips (dev-embedded/libftdi)
dev-games/cegui:devil - Enable image loading via DevIL
dev-games/cegui:irrlicht - Enable the Irrlicht renderer
dev-games/cegui:xerces-c - Enable the Xerces-C++ XML parser module
dev-games/crystalspace:3ds - Enables support for .3DS files in CrystalSpace
dev-games/crystalspace:bullet - include support for Bullet library
dev-games/crystalspace:cal3d - include support for skeleton animation
dev-games/crystalspace:cegui - include support for Crazy Eddie GUI
dev-games/crystalspace:cg - NVIDIA toolkit plugin
dev-games/crystalspace:ode - include support for Open Dynamics Engine
dev-games/guichan:allegro - Build the Allegro frontend
dev-games/ode:double-precision - more precise calculations at the expense of speed
dev-games/ode:gyroscopic - enable gyroscopic term (may cause instability)
dev-games/ogre:cegui - build the CEGUI samples
dev-games/ogre:cg - NVIDIA toolkit plugin
dev-games/ogre:devil - image loading support with DevIL
dev-games/ogre:double-precision - more precise calculations at the expense of speed
dev-games/openscenegraph:fox - Build examples using x11-libs/fox library
dev-games/openscenegraph:gdal - Enable support for sci-libs/gdal library
dev-games/openscenegraph:openinventor - Build OpenInventor plugin
dev-games/openscenegraph:osgapps - Build osg applications
dev-games/openscenegraph:xrandr - Enable support for the X xrandr extension
dev-games/physfs:grp - Enable Build Engine GRP archive support
dev-games/physfs:hog - Enable Descent I/II HOG archive support
dev-games/physfs:mvl - Enable Descent I/II MVL archive support
dev-games/physfs:qpak - Enable Quake I/II QPAK archive support
dev-games/physfs:wad - Enable Doom WAD archive support
dev-games/physfs:zip - Enable ZIP archive support
dev-haskell/gtk2hs:glade - Enable gnome-base/libglade bindings compilation
dev-java/ant:antlr - Enable ANTLR Ant tasks
dev-java/ant:bcel - Enable bcel (bytecode manipulation) Ant tasks
dev-java/ant:commonslogging - Enable commons-logging Ant tasks
dev-java/ant:commonsnet - Enable commons-net Ant tasks
dev-java/ant:jai - Enable JAI (Java Imaging) Ant task
dev-java/ant:javamail - Enable JavaMail Ant task
dev-java/ant:jdepend - Enable Jdepend Ant tasks
dev-java/ant:jmf - Enable JMF (Java Media Framework) Ant tasks
dev-java/ant:jsch - Disable Jsch (ssh, scp and related) Ant tasks
dev-java/ant:log4j - Enable Apache log4j Ant tasks
dev-java/ant:oro - Enable Apache Oro Ant tasks
dev-java/ant:regexp - Enable Apache Regexp Ant tasks
dev-java/ant:resolver - Enable Apache Resolver Ant tasks
dev-java/ant:testutil - Enable optional test util classes
dev-java/antlr:gunit -  gUnit is a "Unit Test" framework for ANTLR grammars 
dev-java/antlr:script - Install a script to run antlr
dev-java/commons-collections:test-framework - Install the test framework
dev-java/commons-logging:avalon-framework - Add optional support for avalon-framework
dev-java/commons-logging:avalon-logkit - Add optional support for avalon-logkit
dev-java/commons-logging:log4j - Add optional support for log4j
dev-java/commons-logging:servletapi - Add optional support for servletapi
dev-java/commons-modeler:commons-digester - Add support for the commons-digester based Mbeans Descriptor source
dev-java/diablo-jdk:jce - Enable Java Cryptographic Extension Unlimited Strength Policy files
dev-java/ecj-gcj:native - Build a native binary along with the jar. Provides faster execution time, but needs about 1G memory and some patience to compile.
dev-java/eclipse-ecj:ant - Support using ecj in Ant builds via dev-java/ant-eclipse-ecj
dev-java/emma:launcher - Install /usr/bin/emma. Collides with sci-biology/emboss.
dev-java/fop:hyphenation - Precompile hyphenation patterns from the dev-java/offo-hyphenation package and install them as fop-hyph.jar
dev-java/fop:jai - Enable jai support
dev-java/fop:jimi - Enable jimi support
dev-java/gjdoc:xmldoclet - Also build support for the xml doclet that generates output in xml instead of the traditional html javadoc.
dev-java/gnu-classpath:alsa - Build with ALSA javax.sound.midi provider
dev-java/gnu-classpath:dssi - Build with DSSI javax.sound.midi provider
dev-java/gnu-classpath:gconf - Build with GConf preferences backend
dev-java/gnu-classpath:gjdoc - Build GJDoc, a documentation generator
dev-java/gnu-classpath:gmp - Build with GMP backend for java.math.BigInteger
dev-java/gnu-classpath:gstreamer - Build with GStreamer javax.sound.sampler provider
dev-java/gnu-classpath:gtk - Build with Gtk+ AWT peers
dev-java/gnu-classpath:qt4 - Build with Qt4 AWT peers
dev-java/gnu-classpath:xml - Build with native XML backend
dev-java/ibm-jdk-bin:javacomm - Enable Java Communications API support
dev-java/icedtea:cacao - Use the CACAO virtual machine instead of HotSpot on x86, amd64 or SPARC architectures.
dev-java/icedtea:hs19 - Use the new version of HotSpot (19).
dev-java/icedtea:nio2 - Enable backport of NIO2 to OpenJDK6.
dev-java/icedtea:nsplugin - Enable browser plugin (NPPlugin), requires also the webstart flag to be enabled.
dev-java/icedtea:nss - Enable NSS security provider support.
dev-java/icedtea:systemtap - Enable SystemTap probes in HotSpot.
dev-java/icedtea:webstart - Enable Web Start support (via NetX).
dev-java/icedtea:xrender - Enable support for using XRender with the AWT libraries.
dev-java/icedtea:zero - Enable the zero assembler port of HotSpot.
dev-java/itext:rtf - Build and provide libraries for rich text format
dev-java/itext:rups - Build and provide GUI for Reading/Updating PDF Syntax
dev-java/jamvm:libffi - use dev-libs/libffi to call native methods
dev-java/jcs:admin - Enable JCS Admin servlets
dev-java/jdbc-jaybird:jni - Build/Install JDBC Type 2 native components
dev-java/jdbc-mysql:c3p0 - Enable c3p0 support
dev-java/jdbc-mysql:log4j - Enable log4 support
dev-java/jdbc-oracle-bin:dms - Enable support for the Oracle Dynamic Monitoring Service
dev-java/jdbc-oracle-bin:ons - Enable support for the Oracle Notification Services (ONS) deamon
dev-java/jython:servletapi - Add optional support for servlet-api
dev-java/log4j:javamail - Build the SMTPAppender
dev-java/log4j:jms - Build the JMSAppender
dev-java/log4j:jmx - Build org.apace.log4j.jmx
dev-java/proguard:ant - Ant task for using ProGuard in build.xml scripts
dev-java/proguard:j2me - Adds support for J2ME Wireless Toolkit
dev-java/qtjambi:phonon - Enable bindings to QT Phonon
dev-java/qtjambi:webkit - Enable bindings to QT Webkit
dev-java/qtjambi:xmlpatterns - Enable bindings to QT xmlpatterns
dev-java/rxtx:lfd - Installs and uses LockFileServer daemon (lfd)
dev-java/sun-jdk:derby - Enable Installation of Bundled Derby (Java DB)
dev-java/sun-jdk:jce - Enable Java Cryptographic Extension Unlimited Strength Policy files
dev-java/sun-jre-bin:jce - Enable Java Cryptographic Extension Unlimited Strength Policy files
dev-java/swt:xulrunner - Embedded browser support via xulrunner-1.9 (1.8 for swt-3.3). Xulrunner 2.0 is not supported, will be replaced by webkit in 3.7.
dev-lang/erlang:hipe - HIgh Performance Erlang extension
dev-lang/erlang:kpoll - Enable kernel polling support
dev-lang/erlang:sctp - Support for Stream Control Transmission Protocol
dev-lang/gdl:hdf - Adds support for the Hierarchical Data Format
dev-lang/gdl:udunits - Support for manipulating units of physical quantities
dev-lang/gforth:force-reg - Enable a possibly unstable GCC flag for possibly large performance gains
dev-lang/ghc:binary - Install the binary version directly, rather than using it to build the source version.
dev-lang/ghc:ghcbootstrap - Internal: Bootstrap GHC from an existing GHC installation.
dev-lang/icc:eclipse - Install the dev-util/eclipse-sdk plugins
dev-lang/icc:idb - Install the Intel Debugger
dev-lang/icc:ipp - Install the Intel Integrated Primitive
dev-lang/icc:mkl - Install the Intel Math Kernel Library
dev-lang/icon:iplsrc - install the icon programming library source
dev-lang/idb:eclipse - Install the dev-util/eclipse-sdk plugins
dev-lang/idb:icc - Use dev-lang/icc to install idb (default)
dev-lang/idb:ifc - Use dev-lang/ifc to install idb
dev-lang/ifc:idb - Install the Intel Debugger
dev-lang/ifc:mkl - Install the Intel Math Kernel Library
dev-lang/lisaac:vim - install a syntax file for vim
dev-lang/logtalk:fop - Support for generating pdf documentation using fop
dev-lang/logtalk:gnupl - Support GNU Prolog back-end compiler
dev-lang/logtalk:qupl - Support Qu-Prolog back-end compiler
dev-lang/logtalk:swipl - Support SWI-Prolog back-end compiler
dev-lang/logtalk:xsbpl - Support XSB back-end compiler
dev-lang/logtalk:xslt - Support for generating html documentation using xslt
dev-lang/logtalk:yappl - Support YAP back-end compiler
dev-lang/lua:deprecated - make deprecated data structures/routines available
dev-lang/mercury:erlang - Support Mercury Erlang grade
dev-lang/mlton:binary - install a binary version (need to do this once to bootstrap, until smlnj is supported)
dev-lang/mono:moonlight - Generate Moonlight 2.1 assemblies
dev-lang/mono:profile4 - Include partial support for C# 4.0 and some of the upcoming .NET 4.0 APIs.
dev-lang/mono:xen - Make mono generate code that is considerably faster on xen VMs but slightly slower on for normal systems.
dev-lang/perl:ithreads - Enable Perl threads, has some compatibility problems
dev-lang/perl:perlsuid - Enable Perl SUID install. Has some risks associated.
dev-lang/php:cli - Enable CLI SAPI
dev-lang/php:concurrentmodphp - Make it possible to load both mod_php4 and mod_php5 into the same Apache2 instance (experimental)
dev-lang/php:discard-path - Switch on common security setting for CGI SAPI
dev-lang/php:embed - Enable embed SAPI
dev-lang/php:enchant - Add supports Enchant spelling library.
dev-lang/php:fdftk - Add supports for Adobe's FDF toolkit.
dev-lang/php:fileinfo - Add fileinfo extension support
dev-lang/php:filter - Add filter extension support
dev-lang/php:force-cgi-redirect - Switch on common security setting for CGI SAPI
dev-lang/php:fpm - Enable the FastCGI Process Manager SAPI
dev-lang/php:hash - Enable the hash extension
dev-lang/php:intl - Enables the intl extension for extended internalization support
dev-lang/php:json - Enable JSON support
dev-lang/php:ldap-sasl - Add SASL support for the PHP LDAP extension
dev-lang/php:mysqlnd - Use native driver for mysql, mysqli, PDO_Mysql
dev-lang/php:pcre - Adds support for Perl Compatible Regular Expressions (deprecated: always "on" in php 5.3)
dev-lang/php:pdo - Enable the bundled PDO extensions
dev-lang/php:phar - Enables the phar extension to provide phar archive support
dev-lang/php:pic - Force shared modules to build as PIC on x86 (speed tradeoff with memory usage)
dev-lang/php:reflection - Enable the reflection extension (Reflection API) (deprecated: always "on" in php 5.3)
dev-lang/php:spl - Adds support for the Standard PHP Library (deprecated: always "on" in php 5.3)
dev-lang/php:suhosin - Add Suhosin support (patch and extension from http://www.suhosin.org/)
dev-lang/php:xmlreader - Enable XMLReader support
dev-lang/php:xmlwriter - Enable XMLWriter support
dev-lang/php:zip - Enable ZIP file support
dev-lang/python:threads - Enable threading support. (DON'T DISABLE THIS UNLESS YOU KNOW WHAT YOU'RE DOING)
dev-lang/python:wide-unicode - Enable wide Unicode implementation which uses 4-byte Unicode characters. Switching of this USE flag changes ABI of Python and requires reinstallation of many Python modules. (DON'T DISABLE THIS UNLESS YOU KNOW WHAT YOU'RE DOING)
dev-lang/python:wininst - Install Windows executables required to create an executable installer for MS Windows.
dev-lang/qu-prolog:pedro - Pedro subscription/notification communications system
dev-lang/ruby:libedit -  Use the dev-libs/libedit library to provide the readline extension, used for instance by the irb tool. This flag will take precedence over the readline USE flag. If neither libedit nor readline USE flags are enabled, the readline extension will not be built (and irb will lose line editing functionality). 
dev-lang/ruby:rdoc -  Install dev-ruby/rdoc after installing Ruby. 
dev-lang/ruby:readline -  Use the sys-libs/readline library to provide the readline extension, used for instance by the irb tool. This flag is meaningful only if the libedit USE flag is disabled. If neither libedit nor readline USE flags are enabled, the readline extension will not be built (and irb will lose line editing functionality). 
dev-lang/ruby:rubytests -  Install ruby tests that can only be run after ruby is installed 
dev-lang/ruby:yaml -  Use the dev-libs/libyaml library to build the psych extension, available since Ruby 1.9.2_rc2, in alternative to the bundled syck-based parser. 
dev-lang/ruby-enterprise:fastthreading -  EXPERIMENTAL Enables fast threading routines. Removes support for callcc. 
dev-lang/ruby-enterprise:libedit -  Use the dev-libs/libedit library to provide the readline extension, used for instance by the irb tool. This flag will take precedence over the readline USE flag. If neither libedit nor readline USE flags are enabled, the readline extension will not be built (and irb will lose line editing functionality). 
dev-lang/ruby-enterprise:readline -  Use the sys-libs/readline library to provide the readline extension, used for instance by the irb tool. This flag is meaningful only if the libedit USE flag is disabled. If neither libedit nor readline USE flags are enabled, the readline extension will not be built (and irb will lose line editing functionality). 
dev-lang/ruby-enterprise:rubytests -  Install ruby tests that can only be run after ruby is installed 
dev-lang/ruby-enterprise:tcmalloc -  Add support for TCMalloc provided by dev-util/google-perftools 
dev-lang/scala:binary - Install from (Gentoo-compiled) binary instead of building from sources. Set this when you run out of memory during build.
dev-lang/spidermonkey:threadsafe - Build a threadsafe version of spidermonkey
dev-lang/swig:ccache - build ccache-swig(a fast compiler cache)
dev-lang/vala:coverage - Enable coverage analysis
dev-lang/vala:vapigen - Enable vala's library binding generator
dev-libs/DirectFB:sysfs - Add support for the sysfs filesystem (requires Linux-2.6+)
dev-libs/STLport:boost - Enable the usage of dev-libs/boost
dev-libs/ace:ciao - Include Component Intergraced Ace ORB into the build of ace
dev-libs/ace:tao - Include the ACE ORB (CORBA stuff) (called tao) into the build of ace
dev-libs/apr:older-kernels-compatibility - Enable binary compatibility with older kernels
dev-libs/apr:urandom - Use /dev/urandom instead of /dev/random
dev-libs/atk:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/boolstuff:static - Enable static linking
dev-libs/boost:eselect - Run "eselect boost update" even if version is already selected
dev-libs/boost:tools - Build and install the boost tools (bcp, quickbook, inspect, wave)
dev-libs/crypto++:sse3 - Enable optimizations via sse3 assembly code
dev-libs/cyberjack:fox - Enable installation of x11-libs/fox based fxcyberjack program
dev-libs/cyberjack:pcsc-lite - Enable installation of sys-apps/pcsc-lite driver
dev-libs/cyrus-sasl:authdaemond - Enable Courier-IMAP authdaemond's unix socket support (net-mail/courier-imap, mail-mta/courier) 
dev-libs/cyrus-sasl:ntlm_unsupported_patch - Add NTLM net-fs/samba NOT supported patch
dev-libs/cyrus-sasl:sample - Build sample client and server
dev-libs/cyrus-sasl:srp - Enable SRP
dev-libs/cyrus-sasl:urandom - Use /dev/urandom instead of /dev/random
dev-libs/e_dbus:bluetooth - Enable interfacing with net-wireless/bluez DBus API.
dev-libs/e_dbus:connman - Enable interfacing with net-misc/connman DBus API.
dev-libs/e_dbus:hal - Enable interfacing with sys-apps/hal DBus API.
dev-libs/e_dbus:libnotify - Enable interfacing with x11-libs/libnotify DBus API.
dev-libs/e_dbus:ofono - Enable interfacing with net-misc/ofono DBus API.
dev-libs/e_dbus:test-binaries - Enable building of test binaries for enabled features
dev-libs/e_dbus:ukit - Enable interfacing with sys-power/upower and sys-fs/udisks DBus API.
dev-libs/ecore:ares - Enables support for asynchronous DNS using the net-dns/c-ares library
dev-libs/ecore:evas - Provides easy to use canvas by gluing media-libs/evas and various input/output systems.
dev-libs/ecore:glib - Enable dev-libs/glib eventloop support
dev-libs/ecore:inotify - Enable support for inotify
dev-libs/ecore:tslib - Build with tslib support for touchscreen devices.
dev-libs/ecore:xprint - Enable X11 Xprint support
dev-libs/eggdbus:largefile - Support for large files
dev-libs/eina:default-mempool - By default use system's allocator (pass-through) instead of custom choice for Eina's own data structures.
dev-libs/eina:mempool-buddy - Compile "buddy" memory pool allocation.
dev-libs/eina:mempool-chained - Compile "chained-pool" memory pool allocation.
dev-libs/eina:mempool-fixed-bitmap - Compile "fixed-bitmap" memory pool allocation.
dev-libs/eina:mempool-pass-through - Compile "pass-through" (system's malloc) memory pool allocation.
dev-libs/elfutils:lzma - Support automatic decompression of LZMA-compressed files and kernel images.
dev-libs/fcgi:html - Install HTML documentation
dev-libs/ferrisloki:stlport - Include support for dev-libs/STLport
dev-libs/geoip:perl-geoipupdate - Install pure perl version of geoipupdate, with Proxy Server support via via the "http_proxy" environment variable and easy to customize.
dev-libs/glib:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/json-glib:coverage - Enable coverage analysis
dev-libs/json-glib:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/klibc:n32 - Force klibc to 32bit if on mips64 if not n32 userland
dev-libs/libburn:track-src-odirect - Read track input with O_DIRECT (see man 2 open), this may deliver a better write performance in some situations
dev-libs/libcdio:minimal -  Only build the libcdio library and little more, just to be used to link against from multimedia players. With this USE flag enabled, none of the command-line utilities are built, nor is the CDDA library. 
dev-libs/libgdata:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/libgee:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/libgpg-error:common-lisp - Install common-lisp files
dev-libs/libisoburn:external-filters - Allow the use of external processes as file content filters (Note: this is a potential security risk)
dev-libs/libisoburn:external-filters-setuid - Also allow the use of external setuid processes as file content filters (Note: this is a potential security risk)
dev-libs/libisofs:verbose-debug - Enable verbose debug messages
dev-libs/libjit:interpreter - Enable the libjit interpreter
dev-libs/libjit:long-double - Enable the use of long double for jit_nfloat
dev-libs/libmail:apop - Enables the APOP authentication method
dev-libs/libmemcached:hsieh - Use Hsieh hash algorithm.
dev-libs/libmix:no-net2 - Disable support for virtual/libpcap and net-libs/libnet
dev-libs/libpcre:recursion-limit -  Limit match recursion to 8192; if disabled, the default limit is used, which is the same as the match limit. 
dev-libs/libprelude:easy-bindings - Enable support for high level bindings (available for C++, Perl, Python)
dev-libs/libprelude:swig - Enable rebuild of swig bindings
dev-libs/libpreludedb:swig - Enable rebuild of swig bindings
dev-libs/libsqlora8:orathreads - Use Oracle threads
dev-libs/libtomcrypt:libtommath - Use the portable math library (dev-libs/libtommath)
dev-libs/libtomcrypt:tomsfastmath - Use the optimized math library (dev-libs/tomsfastmath)
dev-libs/libunique:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/log4cxx:smtp - Offer SMTP support via net-libs/libesmtp
dev-libs/nss:utils - Install utilities included with the library
dev-libs/opencryptoki:tpm -  Enable support for Trusted Platform Module (TPM) using app-crypt/trousers 
dev-libs/openct:pcsc-lite - Enable support for sys-apps/pcsc-lite
dev-libs/openobex:irda - Enable IrDA support
dev-libs/opensc:openct - Build using dev-libs/openct compatibility
dev-libs/opensc:pcsc-lite - Build with sys-apps/pcsc-lite
dev-libs/openssl:rfc3779 - Enable support for RFC 3779 (X.509 Extensions for IP Addresses and AS Identifiers)
dev-libs/pkcs11-helper:nss - Enable NSS crypto engine
dev-libs/ppl:lpsol - Build the ppl_lpsol linear programming problem solver
dev-libs/ppl:watchdog - Build the PPL Watchdog library - a C++ library for multiple, concurrent watchdog timers
dev-libs/seed:dbus - Build the JS module for sys-apps/dbus and dev-libs/dbus-glib
dev-libs/seed:mpfr - Build the JS module for dev-libs/mpfr
dev-libs/seed:profile - Build support for profiling dev-libs/seed for development purposes
dev-libs/seed:xml - Build JS module for dev-libs/libxml2
dev-libs/soprano:clucene - Enable dev-cpp/clucene backend support.
dev-libs/soprano:java - Enables support for virtual/jre-1.6.0 (sesame2) storage backend.
dev-libs/soprano:raptor - Enables support for media-libs/raptor RDF parser/serializer.
dev-libs/soprano:redland - Enables support for the dev-libs/redland storage backend (really slow one).
dev-libs/soprano:virtuoso - Enables support for dev-db/virtuoso storage backend.
dev-libs/tinyxml:stl - Compile with TIXML_USE_STL support
dev-libs/totem-pl-parser:introspection - Use dev-libs/gobject-introspection for introspection
dev-libs/udis86:pic - Force shared libraries to be built as PIC
dev-libs/xerces-c:iconv - Use iconv (virtual/libiconv) as message loader and transcoder (in general it would be possible to use iconv only as message loader and something else like icu or the native method as transcoder and vice-versa, but this is a less common case and hard to handle)
dev-libs/xerces-c:libwww - Use the net-libs/libwww library for fetching URLs, instead of the builtin method
dev-libs/xerces-c:threads - Enable threading support through pthread (or other libraries on AIX, IRIX, HPUX, Solars). Highly recommended
dev-libs/xml-security-c:xalan - Enable support for XSLT and XPath parsing by dev-libs/xalan-c
dev-libs/xmlrpc-c:abyss - Build the Abyss mini web-server.
dev-libs/xmlrpc-c:threads - Controls whether to build the Abyss web-server with pthreads or fork 'threading'.
dev-libs/xmlrpc-c:tools - Build the xmlrpc* tools.
dev-libs/xmlsec:gcrypt - Install xmlsec-gcrypt library
dev-libs/xmlsec:gnutls - Install xmlsec-gnutls library
dev-libs/xmlsec:nss - Install xmlsec-nss library
dev-libs/xmlsec:openssl - Install xmlsec-openssl library
dev-libs/xqilla:faxpp - Use dev-libs/faxpp instead of Xerces-C for certain tasks
dev-libs/xqilla:htmltidy - Use app-text/htmltidy when parsing HTML
dev-libs/yaz:ziffy - Install ziffy, a promiscuous Z39.50 APDU sniffer
dev-lisp/abcl:clisp - Build Armed Bear Common Lisp using GNU CLISP
dev-lisp/abcl:cmucl - Build Armed Bear Common Lisp using CMU Common Lisp
dev-lisp/abcl:jad - Enable support for disassembling compiled code using JAD
dev-lisp/clisp:hyperspec - Use local hyperspec instead of online version
dev-lisp/clisp:new-clx - Build CLISP with support for the NEW-CLX module which is a C binding to the Xorg libraries
dev-lisp/clisp:pari - Build CLISP with support for the PARI Computer Algebra System
dev-lisp/clisp:svm - Build CLISP with support for the Support Vector Machine module
dev-lisp/cmucl:nosource - Don't include source code for CMUCL in installation
dev-lisp/ecls:gengc - Use generational garbage collection (experimental)
dev-lisp/ecls:precisegc - Use type information during garbage collection (experimental)
dev-lisp/gcl:ansi - Build a GCL with ANSI support (else build a traditional CLtL1 image)
dev-lisp/gcl:custreloc - Build a GCL which uses custom GCL code for linking
dev-lisp/gcl:dlopen - Build a GCL which uses dlopen for linking
dev-lisp/gcl:gprof - Build a GCL with profiling support
dev-lisp/sbcl:cobalt - mips only: use mipsel binary instead of mips big endian binary to bootstrap
dev-lisp/sbcl:ldb - Include support for the SBCL low level debugger
dev-lua/luarocks:curl - Uses net-misc/curl for fetching lua packages instead of net-misc/wget.
dev-lua/luarocks:openssl - Uses dev-libs/openssl for verifying lua packages instead of md5sum.
dev-ml/camlimages:gs - Ghostscript support (app-text/ghostscript-gpl)
dev-ml/lablgtk:glade - Enable libglade bindings compilation.
dev-ml/lablgtk:gnomecanvas - Enable libgnomecanvas bindings compilation.
dev-ml/lablgtk:sourceview - Enable GtkSourceView support
dev-ml/ocamlnet:httpd - Enables net-httpd web server component
dev-ml/ocamlnet:zip - Enables netzip support to read/write gzip data using object channels
dev-perl/App-Nopaste:clipboard - copying of URLs with -x/--copy
dev-perl/App-Nopaste:github - Github authentication
dev-perl/App-Nopaste:pastebin - pastebin.com support
dev-perl/DBIx-Class:admin -  Modules required for the DBIx::Class administrative library 
dev-perl/DBIx-Class:admin_script -  Modules required for the CLI DBIx::Class interface dbicadmin 
dev-perl/DBIx-Class:deploy -  Modules required for "deploy" in DBIx::Class::Storage::DBI and "deploymen_statements" in DBIx::Class::Storage::DBI 
dev-perl/DBIx-Class:replicated -  Modules required for DBIx::Class::Storage::DBI::Replicated 
dev-perl/Eidetic:auth - Enables dev-perl/Apache-AuthTicket based cookie authentication
dev-perl/GD:animgif - Enable animated gif support
dev-perl/Graphics-ColorNames:recommended - Install recommended support modules
dev-perl/HTML-Mason:modperl - Enable www-apache/mod_perl support
dev-perl/PDL:badval - Enable badval support
dev-perl/Panotools-Script:gui -  Installs GUIs for some tools 
dev-perl/Sysadm-Install:hammer - Enable hammer() funtion to run a command in the shell and simulate a user hammering the ENTER key to accept defaults on prompts
dev-php/PEAR-HTTP_Download:minimal - Do not include support for PEAR-MIME_Type
dev-php/PEAR-HTTP_Download:postgres - Send postgres LOBs without buffering
dev-php/PEAR-PHP_Shell:auto-completion - Enable tab-completion
dev-php5/ZendFramework:cli - Enables the CLI
dev-php5/ZendFramework:doc - Installs the documentation
dev-php5/ZendFramework:examples - Installs the examples
dev-php5/ZendFramework:minimal - Installs the minimal version without Dojo toolkit, tests and demos
dev-php5/eaccelerator:contentcache - Enable content caching
dev-php5/eaccelerator:disassembler - Enable the eA disassembler
dev-php5/eaccelerator:doccommentinclusion - If you want eAccelerator to retain doc-comments in internal php structures.
dev-php5/eaccelerator:inode - Use inode-based caching
dev-php5/php-gtk:glade - Enable libglade support
dev-php5/php-gtk:libsexy - Enable libsexy support
dev-php5/php-gtk:mozembed - Enable GtkMozembed support
dev-php5/php-gtk:scintilla - Enable Scintilla support
dev-python/PyFoam:extras - Enable optional dependencies
dev-python/PyQt4:X - Build the QtGui and QtDesigner modules
dev-python/PyQt4:assistant - Build the QtHelp and QtAssistant modules
dev-python/PyQt4:declarative - Build the QtDeclarative module
dev-python/PyQt4:kde - Select media-sound/phonon as Phonon variant needed for KDE
dev-python/PyQt4:multimedia - Build the QtMultimedia module
dev-python/PyQt4:opengl - Build the QtOpenGL module
dev-python/PyQt4:phonon - Build the phonon module
dev-python/PyQt4:sql - Build the QtSql module
dev-python/PyQt4:svg - Build the QtSvg module
dev-python/PyQt4:webkit - Build the QtWebKit module
dev-python/PyQt4:xmlpatterns - Build the QtXmlPatterns module
dev-python/anyvc:bazaar - Add support for Bazaar
dev-python/anyvc:git - Add support for Git
dev-python/anyvc:mercurial - Add support for Mercurial
dev-python/atpy:fits -  Enable support for reading and FITS with dev-python/pyfits. 
dev-python/atpy:votable -  Enable support for reading and VOTABLE with dev-python/vo. 
dev-python/bpython:urwid - Backend based on dev-python/urwid
dev-python/cgkit:3ds - Enable support for importing 3D Studio models
dev-python/dap:server - Enable OpenDAP server support
dev-python/django-extensions:graphviz - Create a diagram of your database entity relationships using dev-python/pygraphviz.
dev-python/django-extensions:s3 - Upload your media files to S3.
dev-python/django-extensions:vcard - Export your users email addresses to the vcard format.
dev-python/docutils:glep - Install support for GLEPs
dev-python/jinja:i18n - Enables support for i18n with dev-python/Babel
dev-python/kaa-base:tls - SSL/TLS support via dev-python/tlslite
dev-python/ldaptor:web - enable the web front end for ldaptor (uses dev-python/nevow)
dev-python/markdown:pygments - Enable fancy pygments support
dev-python/matplotlib:excel - Pull dev-python/xlwt for the exceltools toolkit
dev-python/matplotlib:traits - Pull dev-python/traits for the experimental enthought traits support
dev-python/mpmath:matplotlib - Add support for dev-python/matplotlib
dev-python/numexpr:mkl - Enable support for Intel Vector Math Library, part of sci-libs/mkl.
dev-python/paste:flup - enable support for flup (and therefore for various wgsi servers and middleware)
dev-python/paste:openid - enable OpenID support
dev-python/psycopg:mxdatetime - Enable support for MX DateTime and use it instead of Python's built-in datetime module
dev-python/pygobject:introspection - Use dev-libs/gobject-introspection for introspection
dev-python/pygobject:libffi - Enable support to connect to signals on python objects from C.
dev-python/pylons:genshi - Add optional genshi support
dev-python/pylons:jinja - Add optional jinja support
dev-python/pyyaml:libyaml - enable libyaml support
dev-python/pyzor:pyzord - enable support for pyzord
dev-python/rdflib:redland - enable support for Redland triplestore
dev-python/rdflib:zodb - enable support for Zope Object Database triplestore
dev-python/restkit:cli - Install the restcli command line interface/tool, based on dev-python/ipython
dev-python/spyder:ipython - Add support for dev-python/ipython
dev-python/spyder:matplotlib - Add support for dev-python/matplotlib
dev-python/spyder:numpy - Add support for dev-python/numpy
dev-python/spyder:pyflakes - Add support for dev-python/pyflakes
dev-python/spyder:pylint - Add support for dev-python/pylint
dev-python/spyder:rope - Add support for sci-libs/rope
dev-python/spyder:scipy - Add support for sci-libs/scipy
dev-python/sympy:imaging - Add support for dev-python/imaging
dev-python/sympy:ipython - Add support for dev-python/ipython
dev-python/sympy:mathml - Add support for mathml
dev-python/sympy:texmacs - Add support for app-office/texmacs
dev-python/twisted:serial - include serial port support
dev-python/wxpython:doc - Install HTML wxWidgets docs and wxpython API reference.
dev-python/wxpython:examples - Install interactive demo module browser and sample applets.
dev-python/zsi:twisted - add support for dev-python/twisted
dev-ruby/camping:mongrel - Also install www-servers/mongrel
dev-ruby/nokogiri:ffi -  Use the Foreign Function Interface library (as provided by dev-java/jruby or dev-ruby/ffi depending on the implementation) rather than building a C extension to wrap around the libxml/libxslt interfaces. Note: JRuby always uses the FFI interface as native extensions are not supported. 
dev-ruby/ruby-sdl:image - Enable media-libs/sdl-image support
dev-ruby/ruby-sdl:mixer - Enable media-libs/sdl-mixer support
dev-ruby/ruby-sdl:sge - Enable sdl-sge support
dev-ruby/rubygems:server - Install support for the rubygems server
dev-ruby/sqlite3-ruby:swig - Use dev-lang/swig to generate bindings
dev-scheme/bigloo:bglpkg - Build bglpkg binary, which can be use to access scmpkg servers
dev-scheme/bigloo:calendar - Build the embedded library for calendar programming
dev-scheme/bigloo:crypto - Build the embedded cryptographic library
dev-scheme/bigloo:debug - Enable extra debug codepaths
dev-scheme/bigloo:doc - Install Bigloo Manual (HTML docs of Bigloo and r5rs)
dev-scheme/bigloo:emacs - Build and install the Bigloo Developement Environment for Emacs (aka bee-mode)
dev-scheme/bigloo:gmp - Adds support for dev-libs/gmp (GNU MP library)
dev-scheme/bigloo:gstreamer - Adds support for media-libs/gstreamer
dev-scheme/bigloo:java - Enable the JVM backend for the Bigloo compiler
dev-scheme/bigloo:mail - Mail library for email management (e.g. maildir and imap support)
dev-scheme/bigloo:multimedia - Build multimedia library (e.g. for managing images). Needed for dev-scheme/hop
dev-scheme/bigloo:packrat - Bigloo port of Tony Garnock-Jones' packrat parser
dev-scheme/bigloo:sqlite - Use the system-wide dev-db/sqlite
dev-scheme/bigloo:srfi1 - Build the srfi1 library: List library
dev-scheme/bigloo:srfi27 - Build the srfi27 library: Source of Random Bits (32bit-arch only)
dev-scheme/bigloo:ssl - Adds support for SSL connections through dev-libs/openssl
dev-scheme/bigloo:text - Library for dealing with text (e.g. BibTeX parser)
dev-scheme/bigloo:threads - Enable thread support, it depends on dev-libs/boehm-gc built with threads use flag
dev-scheme/bigloo:web - Library for web programming (e.g. XML, CGI parsers). Needed for dev-scheme/hop
dev-scheme/gauche-gl:cg - Enable NVidia Cg binding
dev-scheme/gauche-gtk:glgd - Enable GL graph draw
dev-scheme/guile:debug-freelist - Include garbage collector freelist debugging code
dev-scheme/guile:debug-malloc - Include malloc debugging code
dev-scheme/guile:deprecated - Enable deprecated features
dev-scheme/guile:discouraged -  (implied by deprecated) enable merely discouraged features
dev-scheme/guile:elisp - Enable Emacs Lisp support
dev-scheme/guile:networking - Include networking interfaces
dev-scheme/guile:regex -  Include regular expression interfaces
dev-scheme/hop:debug - Enables building with debug symbols
dev-scheme/hop:ssl - Enable SSL support for hop
dev-scheme/hop:threads - Enable thread support for hop, it depends on dev-scheme/bigloo built with threads use flag.
dev-scheme/kawa:awt - Assume AWT is available
dev-scheme/kawa:echo2 - Enable support for the Echo2 web toolkit with dev-java/echo2
dev-scheme/kawa:frontend - Build "kawa" front-end program using sys-libs/readline
dev-scheme/kawa:jemacs - Build JEmacs
dev-scheme/kawa:krl - Build BRL emulation and KRL
dev-scheme/kawa:sax - Assume SAX2 is available with dev-java/sax
dev-scheme/kawa:servlets - Build support for generating servlets with dev-java/servletapi
dev-scheme/kawa:swing - Assume Swing is available
dev-scheme/kawa:swt - Assume SWT is available with dev-java/swt
dev-scheme/kawa:xqtests - Support XQuery Test Suite
dev-scheme/plt-scheme:backtrace -  Support GC backtrace dumps 
dev-scheme/plt-scheme:cgc -  Compile and install additional executables which use the conservative garbage collector 
dev-scheme/plt-scheme:llvm -  Add support for compiling to the low-level virtual machine (llvm) 
dev-scheme/scm:arrays - Support for arrays, uniform-arrays and uniform-vectors.
dev-scheme/scm:bignums - Support for large precision integers.
dev-scheme/scm:cautious - SCM will always check the number of arguments to interpreted closures.
dev-scheme/scm:dynamic-linking - Be able to load compiled files while running.
dev-scheme/scm:engineering-notation - Floats to display in engineering notation (exponents always multiples of 3) instead of scientific notation.
dev-scheme/scm:gsubr - generalized c arguments: for arbitrary (more then 11) arguments to C functions.
dev-scheme/scm:inexact - Support for floating point numbers.
dev-scheme/scm:ioext - Commonly available I/O extensions: line I/O, file positioning, file delete and rename, and directory functions.
dev-scheme/scm:macro - C level support for hygienic and referentially transparent macros (syntax-rules macros).
dev-scheme/scm:regex - String regular expression matching.
dev-scheme/scm:unix - Support for: nice, acct, lstat, readlink, symlink, mknod and sync.
dev-tcltk/expect-lite:debug - pull in packages needed for runtime interactive debugger
dev-tcltk/tktreectrl:shellicon - shellicon extension
dev-tex/dot2texi:pgf - Enable support for dev-tex/pgf (The TeX Portable Graphic Format)
dev-tex/dot2texi:pstricks - Enable pstricks support
dev-tex/latex-beamer:lyx - Install with app-office/lyx layouts
dev-util/anjuta:devhelp - Enable devhelp integration
dev-util/anjuta:glade - Build glade plugin for anjuta
dev-util/anjuta:introspection - Use dev-libs/gobject-introspection for introspection
dev-util/anjuta:sourceview - Build sourceview editing plugin for anjuta
dev-util/anjuta:symbol-db - Enable symbol database plugin for anjuta
dev-util/anjuta:vala - Enable support for the Vala programming language
dev-util/astyle:libs - builds and installs both shared and static library interfaces
dev-util/buildbot:irc - Add support for status delivery through an ircbot.
dev-util/buildbot:mail - Add support for watching a maildir for commits.
dev-util/buildbot:manhole - Add support for manhole (debug over ssh)
dev-util/catalyst:ccache - Enables ccache support
dev-util/codeblocks:contrib - Build additional contrib components
dev-util/cppcheck:htmlreport - install cppcheck-htmlreport
dev-util/ctags:ada - Enable Ada support
dev-util/dialog:minimal - Disable library, install command-line program only
dev-util/geany:vte - Enable Terminal support (x11-libs/vte)
dev-util/geany-plugins:enchant - Enable spell checking using enchant
dev-util/geany-plugins:gtkspell - Use gtkspell for dictionary support
dev-util/global:vim - Integrate the GNU GLOBAL source code tag system with Vim
dev-util/google-perftools:debug -  Build a set of libraries with debug support (so-called debugalloc). These are available by default but are not needed unless you're actually developing using tcmalloc. 
dev-util/google-perftools:largepages -  Use (experimental) larger pages for tcmalloc, this increases memory usage, but should speed up the allocation/free operations. 
dev-util/google-perftools:minimal -  Only build the tcmalloc_minimal library, ignoring the heap checker and the profilers. 
dev-util/gtk-doc:highlight - Enable source code highlighting
dev-util/gtk-doc:vim - Enable source code highlighting through app-editors/vim
dev-util/kdevelop:cmake - Enable support for CMake build system
dev-util/kdevelop:okteta - Enable hex editor plugin
dev-util/kdevelop:qmake - Enable support for QMake build system
dev-util/kdevelop:qthelp - Enable support for QtHelp documentation browsing
dev-util/kdevplatform:git - Enable Git version control support
dev-util/kdevplatform:reviewboard - Enable reviewboard support
dev-util/metro:ccache - Enable support for ccache
dev-util/metro:git - Enable support for git snapshots
dev-util/metro:threads - Enable support for pbzip2 tarball packing/unpacking
dev-util/mono-tools:webkit - Use net-libs/webkit-gtk for rendering.
dev-util/nemiver:memoryview - Enable the optional hexadecimal memory inspection with app-editors/ghex.
dev-util/netbeans:keychain - enables support for keychain in netbeans start script
dev-util/nsis:config-log - Enable the logging facility (useful in debugging installers)
dev-util/nvidia-cuda-sdk:cuda -  Build CUDA binaries. 
dev-util/nvidia-cuda-sdk:emulation -  Build binaries for device emulation mode. These binaries will not require a CUDA-capable GPU to run. 
dev-util/nvidia-cuda-sdk:opencl -  Build OpenCL binaries. 
dev-util/nvidia-cuda-toolkit:debugger -  Installs the CUDA debugger. 
dev-util/nvidia-cuda-toolkit:opencl -  Installs OpenCL utilities. 
dev-util/nvidia-cuda-toolkit:profiler -  Installs the NVIDIA CUDA visual profiler. 
dev-util/perf:demangle -  Enable C++ symbol name demangling, using libbfd from sys-devel/binutils. When this flag is enabled, the package will have to be rebuilt after every version bump of binutils. 
dev-util/perf:doc -  Build documentation and man pages. With this USE flag disabled, the --help parameter for perf and its sub-tools will not be available. This is optional because it depends on a few documentation handling tools that are not always welcome on user systems. 
dev-util/perf:perl -  Add support for Perl as a scripting language for perf tools. 
dev-util/qdevelop:plugins - Build and install additional plugins
dev-util/qt-creator:bineditor - enable bineditor plugin
dev-util/qt-creator:bookmarks - enable bookmarks plugin
dev-util/qt-creator:cmake - enable cmake project manager plugin
dev-util/qt-creator:debugger - enable debugger plugin
dev-util/qt-creator:designer - enable designer plugin
dev-util/qt-creator:fakevim - enable vim-like key bindings plugin
dev-util/qt-creator:git - enable git plugin
dev-util/qt-creator:mercurial - enable mercurial plugin
dev-util/qt-creator:perforce - enable perforce software configuration manager plugin
dev-util/qt-creator:qml - Simple way of building UIs based on Qt Declarative module
dev-util/qt-creator:qtscript - enable qt script editor plugin
dev-util/qt-creator:subversion - enable subversion plugin
dev-util/radare:gui -  Enable the graphical user interface of radare (broken) 
dev-util/radare:vala -  Enable support for the vala programming language 
dev-util/schroot:btrfs - Enable support for chroots using btrfs snapshots.
dev-util/schroot:dchroot - Enables the building of a wrapper named "dchroot", replacing sys-apps/dchroot.
dev-util/schroot:lvm - Enable support for chroots using LVM snapshots.
dev-util/strace:aio -  Enable dev-libs/libaio support for tracing Asynchronous I/O operations 
dev-util/universalindentgui:html - Add support for HTML files
dev-vcs/bzr:sftp - Enable sftp support
dev-vcs/bzr-gtk:gconf - Enable GConf support
dev-vcs/bzr-gtk:gpg - Support signing with GnuPG.
dev-vcs/bzr-gtk:nautilus - Integrate with Nautilus file manager
dev-vcs/bzr-gtk:sourceview - Enable GtkSourceView support
dev-vcs/cvs:server - Enable server support
dev-vcs/cvs2svn:bazaar - Support for dev-vcs/bzr
dev-vcs/cvs2svn:git - Support for dev-vcs/git
dev-vcs/git:blksha1 - Use the new optimized SHA1 implementation.
dev-vcs/git:cgi - Install gitweb too
dev-vcs/git:gtk - Include the gitview contrib tool.
dev-vcs/git:mozsha1 - Makes git use an optimized SHA1 routine from Mozilla that should be fast on non-x86 machines.
dev-vcs/git:ppcsha1 - Make use of a bundled routine that is optimized for the PPC arch.
dev-vcs/git:subversion - Include git-svn for dev-vcs/subversion support.
dev-vcs/git:webdav - Adds support for push'ing to HTTP repositories via DAV.
dev-vcs/gitolite-gentoo:contrib - Install user-contributed files
dev-vcs/mercurial:bugzilla - Support bugzilla integration.
dev-vcs/mercurial:gpg - Support signing with GnuPG.
dev-vcs/mercurial:tk - Install dev-lang/tk for hgk script.
dev-vcs/qct:bazaar -  Support for dev-vcs/bzr 
dev-vcs/qct:mercurial -  Support for dev-vcs/mercurial 
dev-vcs/qct:monotone -  Support for dev-vcs/monotone 
dev-vcs/rabbitvcs:cli - Eanble console based frontend
dev-vcs/rabbitvcs:diff - Use for diff command dev-util/meld
dev-vcs/rabbitvcs:gedit - Enable plugin for app-editors/gedit
dev-vcs/rabbitvcs:nautilus - Enable extension for gnome-base/nautilus
dev-vcs/rabbitvcs:thunar - Enable extension for xfce-base/thunar
dev-vcs/subversion:ctypes-python - Build and install Ctypes Python bindings
dev-vcs/subversion:dso - Enable runtime module search
dev-vcs/subversion:extras - Install extra scripts (examples, tools, hooks)
dev-vcs/subversion:webdav-neon - Enable WebDAV support using net-libs/neon
dev-vcs/subversion:webdav-serf - Enable WebDAV support using net-libs/serf
dev-vcs/svk:log4p - Enable perl logger support
dev-vcs/svk:pager - Enable perl pager selection support
dev-vcs/svk:patch - Enable patch creation, import support
games-action/abuse:demo - Use the demo data instead of the full game
games-action/abuse:levels - Install user-created levels (fRaBs)
games-action/abuse:sounds - Install optional sound data
games-action/chromium:mixer -  Enables media-libs/sdl-mixer sound backend instead of media-libs/openal one. 
games-action/d1x-rebirth:awe32 - Enable AWE32 support
games-action/d1x-rebirth:demo - Use the demo data instead of the full game
games-action/d1x-rebirth:mixer - Enable mixer support
games-action/d1x-rebirth:mpu401 - Enable MPU401 music support
games-action/d2x-rebirth:awe32 - Enable AWE32 support
games-action/d2x-rebirth:mpu401 - Enable MPU401 music support
games-action/openlierox:breakpad -  Compile with support for breakpad crash reporting system 
games-action/teeworlds:server - Enable compilation of server
games-arcade/bomns:editor - enables building the level editor
games-arcade/burgerspace:network - Enable client-server support
games-arcade/jumpnbump:music - Enable playing of background music
games-arcade/lbreakout2:themes - Install additional themes
games-arcade/moleinvasion:music - Download and install the music files
games-arcade/slimevolley:net - Enable network support
games-arcade/smc:music - Download and install the music files
games-arcade/stepmania:force-oss - Force using OSS
games-arcade/triplexinvaders:psyco - psyco python accelerator
games-arcade/tuxanci:sound - Enable sound
games-arcade/ultrastar-ng:songs - Install a few demo songs
games-arcade/ultrastar-ng:video - Enable smpeg video support
games-board/chessdb:tb4 - Install 4 pieces table bases
games-board/crafty:no-opts - Don't try to enable crazy CFLAG options
games-board/freedoko:backgrounds - Install additional background images
games-board/freedoko:gnomecards - Install the gnome-games card set
games-board/freedoko:kdecards - Install the KDE card set
games-board/freedoko:net - Enable network game support
games-board/freedoko:openclipartcards - Install the openclipartcards card set
games-board/freedoko:pysolcards - Install the PySol card set
games-board/freedoko:xskatcards - Install the XSkat card set
games-board/grhino:gtp - Install the GTP (Go/Game Text Protocol) frontend
games-board/pasang-emas:extras - Install some extra themes
games-board/pysolfc:extra-cardsets - Install extra cardsets
games-board/pysolfc:sound - Enable sound support usingdev-python/pygame
games-board/spider:athena - Enable athena widgets
games-board/xboard:default-font - Install the default font that xboard uses
games-board/xboard:zippy - Enable experimental zippy client
games-emulation/generator:sdlaudio - Enable SDL Audio
games-emulation/snes9x:netplay - Enable playing ROMs over the network (not recommended)
games-emulation/snes9x:xrandr - Enable support for the X xrandr extension
games-emulation/xmess:net - Add network support
games-engines/frobtads:tads2compiler - Build TADS2 compiler
games-engines/frobtads:tads3compiler - Build TADS3 compiler
games-engines/scummvm:fluidsynth - compile with support for fluidsynth
games-fps/darkplaces:cdsound - Enables using CD audio in the engine
games-fps/darkplaces:demo - Uses the demo data from quake1 (quake1-demodata)
games-fps/darkplaces:lights - Install and setup the updated light maps
games-fps/darkplaces:textures - Install and setup the updated textures
games-fps/doom-data:doomsday - Add wrapper to run it within doomsday
games-fps/doom3:roe - Adds support for the Resurrection of Evil expansion
games-fps/duke3d:demo - Install the demo files
games-fps/duke3d:pic - disable optimized assembly code that is not PIC friendly
games-fps/ezquake-bin:security - install the security module needed for some servers
games-fps/freedoom:doomsday - Add wrapper to run it within doomsday
games-fps/nexuiz:maps - Install the community map pack
games-fps/quake2-icculus:demo - Install the demo files (quake2-demodata) and configure for use
games-fps/quake2-icculus:qmax - Build the pretty version (quake max)
games-fps/quake2-icculus:rogue - Build support for the 'Ground Zero' Mission Pack (rogue)
games-fps/quake2-icculus:xatrix - Build support for the 'The Reckoning' Mission Pack (xatrix)
games-fps/quake3:teamarena - Adds support for Team Arena expansion pack
games-fps/quake3-bin:teamarena - Adds support for Team Arena expansion pack
games-fps/qudos:demo - Install the demo files (quake2-demodata) and configure for use
games-fps/qudos:mods - Build support for the quake2 mission packs
games-fps/qudos:qmax - Build the pretty version (quake max)
games-fps/qudos:textures - Install the enhanced textures (quake2-textures)
games-fps/rott:demo - Install the shareware version
games-fps/unreal-tournament-goty:S3TC - Add the extra fancy textures to UT ... only works on certain cards (nvidia/ati/s3)
games-fps/warsow:angelscript - Enable AngelScript support
games-fps/warsow:irc - Enable IRC support
games-fps/worldofpadman:maps - Install extra maps (PadPack)
games-kids/gcompris:gnet - will let GCompris fetch content from a web server
games-puzzle/cuyo:music - Enable playing of background music
games-puzzle/jag:editor - Install level editor
games-puzzle/jag:extras - Install additional graphics
games-puzzle/xlogical:alt_gfx - Use alternate graphics which are closer to the original Amiga version
games-roguelike/angband:sound - Enable and install sounds
games-rpg/daimonin-client:music - Install extra music
games-rpg/drascula:audio - Install optional audio files
games-rpg/eternal-lands-data:bloodsuckermaps - Will install Bloodsucker's Maps in place of the official map files.
games-rpg/eternal-lands-data:music - Adds in-game music.
games-rpg/eternal-lands-data:sound - Adds in-game sound effects.
games-rpg/kqlives:cheats - Enable cheating mode
games-rpg/nwn:hou - Install the Hordes of the Underdark expansion pack
games-rpg/nwn:sou - Installs the Shadows of Undrentide expension pack
games-rpg/nwn-data:hou - Install the Hordes of the Underdark expansion pack
games-rpg/nwn-data:nowin - For those people who cant grab the 1.2 gigs of data files from a windows partition
games-rpg/nwn-data:sou - Installs the Shadows of Undrentide expension pack
games-simulation/openttd:aplaymidi - Enables midi music in game, using aplaymidi as an external player
games-simulation/openttd:dedicated - Build only the openttd server, and not the client.
games-simulation/openttd:lzo - Enables LZO compression for savegames. This is only needed to load extremely old savegames. (versions before 0.2)
games-simulation/openttd:openmedia - Enables the free open media sets: OpenGFX, OpenSFX, OpenMSX, removing the requirement for proprietary TTD assets to play OpenTTD.
games-simulation/singularity:music - Install music files
games-sports/xmoto:editor - Depend on inkscape, scripts to convert svg to level (svg2lvl)
games-strategy/dark-oberon:fmod - Add sound support (fmod)
games-strategy/defcon-demo:system-libs - Use system libraries instead of the ones included in the upstream distribution.
games-strategy/freeciv:auth - Add authentication capability
games-strategy/freeciv:ggz - Add support for GGZ Gaming Zone
games-strategy/freeciv:sound - Add support for sound provided by media-libs/sdl-mixer
games-strategy/glest:editor - Also install a level editor
games-strategy/heroes3:maps - Installs optional map data
games-strategy/heroes3:music - Installs optional music data
games-strategy/heroes3:sounds - Installs optional sound data
games-strategy/naev:mixer -  Enables media-libs/sdl-mixer sound backend in addition to media-libs/openal one. 
games-strategy/ufo-ai:editor - Build map editor
games-strategy/uqm:music - download and install music files (large)
games-strategy/uqm:remix - download and install music remix files (large)
games-strategy/uqm:voice - download and install voice files (large)
games-strategy/wesnoth:server - Enable compilation of server
games-strategy/wesnoth:tinygui - enable GUI reductions for resolutions down to 320x240 (PDAs)
games-strategy/x2:bonusscripts - Add bonus scripts
games-strategy/x2:dynamic - Use dynamic binaries instead of static
games-strategy/x2:langpacks - Install additional language packs
games-strategy/x2:modkit - Install the modkit
games-util/gslist:web - Enable the web interface
games-util/xboxdrv:daemon - Install xboxdrv-daemon (and its dependencies)
gnome-base/dconf:introspection - Use dev-libs/gobject-introspection for introspection
gnome-base/dconf:vala - Add support for dev-lang/vala
gnome-base/gconf:introspection - Use dev-libs/gobject-introspection for introspection
gnome-base/gdm:consolekit - Allow proper handling of removable media according to who is actually present on the machine.
gnome-base/gdm:dmx - Enables Distributed Multihead X (DMX) support
gnome-base/gdm:remote - Enables support for secure remote connections
gnome-base/gdm:xklavier - Use x11-libs/libxklavier for keyboard management
gnome-base/gnome-applets:battstat - Enable deprecated battery applet for people unable to use gnome-extra/gnome-power-manager instead.
gnome-base/gnome-light:automount - Use gnome-base/gvfs[gdu] for automounting of drives in nautilus
gnome-base/gnome-menus:introspection - Use dev-libs/gobject-introspection for introspection
gnome-base/gnome-mount:nautilus - Enables the Nautilus plugin
gnome-base/gnome-panel:bonobo - Enable Bonobo compatibility modules for applets still not ported to DBUS.
gnome-base/gnome-panel:introspection - Use dev-libs/gobject-introspection for introspection
gnome-base/gnome-session:splash - Enable gnome splash screen
gnome-base/gvfs:archive - Enables support for accessing files in archives transparently via app-arch/libarchive
gnome-base/gvfs:fuse - Enables fuse mount points in $HOME/.gvfs for legacy application access
gnome-base/gvfs:gdu - Enable sys-apps/gnome-disk-utility integration
gnome-base/gvfs:http - Enable the HTTP/DAV backend using net-libs/libsoup-gnome
gnome-base/gvfs:iphone - Enables support for the iPhone and iPod touch
gnome-base/gvfs:udev - Enable udev base replacement code for cdda feature
gnome-base/libgnomecanvas:glade - Enable glade support
gnome-base/librsvg:tools - Build miscellaneous tools
gnome-base/nautilus:introspection - Use dev-libs/gobject-introspection for introspection
gnome-extra/avant-window-navigator:vala - Enables support for applets written in dev-lang/vala.
gnome-extra/avant-window-navigator:xfce - Enables support for the XFCE 4 desktop environment
gnome-extra/avant-window-navigator-extras:webkit - Enables support for net-libs/webkit-gtk.
gnome-extra/evolution-data-server:weather - Enable optional weather calendar support.
gnome-extra/file-browser-applet:gtkhotkey - Enable hotkey support via x11-libs/gtkhotkey
gnome-extra/gget:epiphany - Install epiphany extensions
gnome-extra/gnome-do-plugins:banshee - Enables the Banshee (media-sound/banshee) plugin
gnome-extra/gnome-games:artworkextra - Installs extra artwork for various games
gnome-extra/gnome-games:clutter - Build games that use media-libs/clutter and are written in JavaScript using dev-libs/seed
gnome-extra/gnome-games:sound - Enable sound using media-libs/libcanberra
gnome-extra/gnome-utils:bonobo - Enable applets (gdict one) still not ported to DBUS, requiring deprecated bonobo support in gnome-panel.
gnome-extra/gucharmap:introspection - Use dev-libs/gobject-introspection for introspection
gnome-extra/libgda:canvas - Enables support for x11-libs/goocanvas
gnome-extra/libgda:http - Enable embedded net-libs/libsoup based server
gnome-extra/libgda:introspection - Use dev-libs/gobject-introspection for introspection
gnome-extra/libgda:json - Enable support for JSON format
gnome-extra/libgda:mdb - Enables Microsoft Access DB support
gnome-extra/libgda:sourceview - Enable support for x11-libs/gtksourceview
gnome-extra/libgda:xbase - Enables support for xbase databases (dBase, FoxPro, etc.)
gnome-extra/libgsf:gtk - Enable use of gdk in thumbnailer
gnome-extra/libgsf:thumbnail - Enable libgsf supported formats thumbnailer
gnome-extra/music-applet:mpd - Enable MPD support
gnome-extra/nautilus-sendto:gajim - Enables support for net-im/gajim
gnome-extra/nautilus-sendto:mail - Enables support for mailto using gnome-extra/evolution-data-server
gnome-extra/nautilus-sendto:pidgin - Enables support for net-im/pidgin
gnome-extra/nautilus-sendto:upnp - Enables support for sending files over upnp using net-libs/gupnp-av
gnome-extra/panflute:mpd - Enable MPD support
gnome-extra/polkit-gnome:introspection - Use dev-libs/gobject-introspection for introspection
gnome-extra/sensors-applet:nvidia - Enables support for sensors on NVidia chips
gnome-extra/yelp:beagle - Enables support for the Beagle (app-misc/beagle) desktop search tool
gnome-extra/yelp:lzma - Enables support for LZMA compressed info and man pages
gnome-extra/zenity:compat - Installs gdialog for compatibility with older shell scripts which uses dev-lang/perl
gnustep-apps/cdplayer:preferences - Use gnustep-apps/preferences for preferences setting
gnustep-apps/cdplayer:systempreferences - Use gnustep-apps/systempreferences for preferences setting
gnustep-apps/gnumail:emoticon - Enable extra Emoticon Bundle to see smiley's in e-mail messages
gnustep-base/gnustep-back-art:xim - Enable X11 XiM input method
gnustep-base/gnustep-back-cairo:xim - Enable X11 XiM input method
gnustep-base/gnustep-back-xlib:xim - Enable X11 XiM input method
gnustep-base/gnustep-base:libffi - Use dev-libs/libffi instead of dev-libs/ffcall
gnustep-base/gnustep-make:native-exceptions - Enables use of the native Objective-C exception support (@try/@catch/@finally) built-in objective-c exceptions with compilers that support it 
gpe-base/gpe:games - Builds and installs GPE games.
kde-base/ark:archive - Enable support for a variety of archive formats through libarchive
kde-base/cantor:R - Enable R backend support
kde-base/cantor:ps - Enable rendering EPS files
kde-base/dolphin:thumbnail -  Enables video thumbnails generation for kde-base/dolphin file manager. 
kde-base/granatier:gluon - Adds support for media-libs/gluon (recommended) instead of x11-libs/qt-multimedia
kde-base/gwenview:kipi - Support for the KDE Image Plugin Interface.
kde-base/kalzium:editor - Enable the embedded molecule editor/viewer
kde-base/kalzium:solver - Enable the equation solver
kde-base/kde-meta:sdk - Enable instalation of SDK components
kde-base/kdeartwork-kscreensaver:eigen - Enable various arithmetic screensavers which use Eigen2 for computations.
kde-base/kdebase-kioslaves:sftp - Enable SFTP protocol support using net-libs/libssh
kde-base/kdebindings-csharp:akonadi - Compile bindings for Akonadi.
kde-base/kdebindings-csharp:phonon - Compile bindings for Phonon.
kde-base/kdebindings-csharp:plasma - Compile bindings for KDE's Plasma.
kde-base/kdebindings-csharp:qimageblitz - Compile bindings for media-libs/qimageblitz.
kde-base/kdebindings-csharp:qscintilla - Compile bindings for x11-libs/qscintilla.
kde-base/kdebindings-csharp:webkit - Compile bindings for x11-libs/qt-webkit.
kde-base/kdebindings-meta:csharp - Enable C# language bindings for KDE and Qt
kde-base/kdebindings-perl:akonadi - Compile bindings for Akonadi.
kde-base/kdebindings-perl:attica - Compile bindings for dev-libs/libattica.
kde-base/kdebindings-perl:multimedia - Compile bindings for x11-libs/qt-multimedia.
kde-base/kdebindings-perl:okular - Compile bindings for kde-base/okular.
kde-base/kdebindings-perl:phonon - Compile bindings for Phonon.
kde-base/kdebindings-perl:plasma - Compile bindings for KDE's Plasma.
kde-base/kdebindings-perl:qimageblitz - Compile bindings for media-libs/qimageblitz.
kde-base/kdebindings-perl:qscintilla - Compile bindings for x11-libs/qscintilla.
kde-base/kdebindings-perl:qthelp - Compile bindings for QtHelp from x11-libs/qt-assistant.
kde-base/kdebindings-perl:qwt - Compile bindings for x11-libs/qwt.
kde-base/kdebindings-perl:webkit - Compile bindings for x11-libs/qt-webkit.
kde-base/kdebindings-ruby:akonadi - Compile bindings for Akonadi.
kde-base/kdebindings-ruby:okular - Compile bindings for kde-base/okular.
kde-base/kdebindings-ruby:phonon - Compile bindings for Phonon.
kde-base/kdebindings-ruby:plasma - Compile bindings for KDE's Plasma.
kde-base/kdebindings-ruby:qscintilla - Compile bindings for x11-libs/qscintilla.
kde-base/kdebindings-ruby:qwt - Compile bindings for x11-libs/qwt.
kde-base/kdebindings-ruby:webkit - Compile bindings for x11-libs/qt-webkit.
kde-base/kdelibs:opengl - Enable OpenGL support for Plasma (GLApplet)
kde-base/kdenetwork-meta:ppp - Enable support for net-dialup/ppp.
kde-base/kdeplasma-addons:desktopglobe - Enable Desktop Globe wallpaper using kde-base/marble
kde-base/kdeplasma-addons:qalculate - Enable Qalculate runner using sci-libs/libqalculate
kde-base/kdeplasma-addons:qwt - Enable applets that use x11-libs/qwt:5.
kde-base/kdeplasma-addons:scim - Enable applets that use app-i18n/scim.
kde-base/kdesdk-misc:extras - Build po2xml and swappo tools
kde-base/kdeutils-meta:floppy - Install kde-base/kfloppy to format and create DOS or ext2fs filesystems in a floppy.
kde-base/kdm:consolekit - Enables support for authorization using consolekit
kde-base/kget:bittorrent - Enable bittorrent transfer plugin through net-libs/libktorrent
kde-base/kget:webkit - Enable KdeWebkit browser plugin using kde-misc/kwebkitpart
kde-base/kig:kig-scripting - Support Python scripting
kde-base/konqueror:bookmarks -  Add dependency on bookmark package. 
kde-base/konqueror:thumbnail -  Enables video thumbnails generation for kde-base/konqueror file manager. 
kde-base/kopete:addbookmarks - Automatically add incoming urls to bookmarks.
kde-base/kopete:autoreplace - Automatically replace selected text
kde-base/kopete:contactnotes - Enables writing personal notes for contacts.
kde-base/kopete:gadu - Enable the Gadu protocol handler.
kde-base/kopete:groupwise - Enable the Groupwise protocol handler.
kde-base/kopete:highlight - Allows you to specify highlights on specific events.
kde-base/kopete:history - Enables saving chat history.
kde-base/kopete:jabber - Enable XMPP protocol handler (this is also gmail).
kde-base/kopete:latex - Embed latex formatted text into messages.
kde-base/kopete:meanwhile - Enable the Sametime protocol handler.
kde-base/kopete:msn - Enable "Windows live messenger" protocol support.
kde-base/kopete:nowlistening - Shows song you currently listen to in your status/etc. Bindings for many players.
kde-base/kopete:otr - Allows crypting your chat (drugs and talking nonsense are considered as good alternatives ;]).
kde-base/kopete:pipes - Send messages to external pipe.
kde-base/kopete:privacy - Filter for incoming messages
kde-base/kopete:qq - enable support for the Chinese network protocol.
kde-base/kopete:skype - Enable Skype protocol handler (not fully functional yet).
kde-base/kopete:sms - Enable SMS sendinge functionality.
kde-base/kopete:statistics - Everybody loves statistic graphs, especially cake ones. ;]
kde-base/kopete:testbed - Enable the testbed protocol.
kde-base/kopete:texteffect - Various fancy text effects for your messages (don't ever consider writing us with this enabled ;]).
kde-base/kopete:translator - Translate incoming and outgoing messages.
kde-base/kopete:urlpicpreview - Enables in conversation pictures preview.
kde-base/kopete:webpresence - Show your status and some more information on web.
kde-base/kopete:winpopup - Enable pop-up messages sending on windows. (same as good old "net send" messages ;])
kde-base/kopete:yahoo - Enable yahoo protocol support.
kde-base/kopete:zeroconf - Enable Link-Local Messaging via the bonjour protocol.
kde-base/krdc:rdp - Enable runtime dependency for net-misc/rdesktop
kde-base/kstars:fits - Enable support for the FITS image format through cfitsio
kde-base/kstars:indi - Enable support for Astronomical control library using libindi
kde-base/kttsd:epos - Build a plugin for app-accessibility/epos
kde-base/kttsd:festival - Build a plugin for app-accessibility/festival
kde-base/kttsd:flite - Build a plugin for app-accessibility/flite
kde-base/kttsd:freetts - Build a plugin for app-accessibility/freetts
kde-base/kttsd:mbrola - Build a plugin for app-accessibility/mbrola
kde-base/marble:designer-plugin - Enable designer plugin
kde-base/okular:chm - Enable support for Microsoft Compiled HTML Help files
kde-base/okular:ebook - Add E-Book support
kde-base/okular:ps - Add PostScript support
kde-base/plasma-workspace:google-gadgets - Add google-gadgets support
kde-base/plasma-workspace:qalculate - Enable Qalculate runner using sci-libs/libqalculate
kde-base/plasma-workspace:rss - Enables building RSSNOW plasmoid (requires kde-base/kdepimlibs)
kde-base/powerdevil:pm-utils - Adds support for suspend/resume the system through sys-power/pm-utils
kde-base/pykde4:semantic-desktop - Enables Nepomuk and Soprano python language bindings
kde-base/smoke:akonadi - Compile bindings for Akonadi.
kde-base/smoke:attica - Compile bindings for dev-libs/libattica.
kde-base/smoke:multimedia - Compile bindings for x11-libs/qt-multimedia.
kde-base/smoke:okular - Compile bindings for kde-base/okular.
kde-base/smoke:phonon - Compile bindings for Phonon.
kde-base/smoke:qimageblitz - Compile bindings for media-libs/qimageblitz.
kde-base/smoke:qscintilla - Compile bindings for x11-libs/qscintilla.
kde-base/smoke:qthelp - Compile bindings for QtHelp from x11-libs/qt-assistant.
kde-base/smoke:qwt - Compile bindings for x11-libs/qwt.
kde-base/smoke:webkit - Compile bindings for x11-libs/qt-webkit.
kde-base/solid:wicd - Enable Wicd wired and wireless network manager.
kde-base/step:qalculate - Enable the libqalculate library for unit conversion
kde-misc/kdiff3:konqueror - Enable integration with konqueror
kde-misc/knetworkmanager:consolekit - Enable support for sys-auth/consolekit
kde-misc/knetworkmanager:wicd - Enable the wicd backend
kde-misc/tellico:addressbook - Add support for kdepim addressbook (kabc)
mail-client/alpine:chappa - enhance alpine by applying Eduardo Chappa's patches
mail-client/alpine:onlyalpine - installs only the alpine binary, so it does not collied with app-editors/pico and/or mail-client/pine
mail-client/alpine:passfile - Adds support for caching passwords into a file between sessions
mail-client/alpine:smime - Enable support for S/MIME
mail-client/alpine:topal - Enable support for net-mail/topal
mail-client/balsa:crypt - Adds support for GnuPG encryption
mail-client/balsa:gtkspell - Use gtkspell for dictionary support
mail-client/balsa:rubrica - Adds support for app-office/rubrica addressbook
mail-client/balsa:webkit - Enable webkit based html renderer
mail-client/claws-mail:bogofilter - Build mail-filter/bogofilter plugin
mail-client/claws-mail:dillo - Enables support for inline HTTP email viewing with a plugin (which depends on the www-client/dillo browser)
mail-client/claws-mail:smime - Build plugin for S/MIME support
mail-client/claws-mail:spamassassin - Build mail-filter/spamassassin plugin
mail-client/claws-mail:ssl - Use gnutls for Secure Socket Layer transactions (deprecated, USE=gnutls should be used)
mail-client/evolution:clutter - Build with clutter support for animation effects
mail-client/evolution:connman - Enable net-misc/connman support (requires 'networkmanager' USE flag to be disabled).
mail-client/evolution:crypt - Enable GPG encryption support using app-crypt/gnupg and app-crypt/pinentry
mail-client/evolution:ldap - Enable support for fetching contacts from an LDAP or Active Directory server using net-nds/openldap
mail-client/evolution:networkmanager - Allows Evolution to automagically toggle online/offline mode by talking to net-misc/networkmanager and getting the current network state
mail-client/evolution:pda - Enable support for syncing Evolution Calendar and Addressbooks with PDAs using app-pda/gnome-pilot and app-pda/gnome-pilot-conduit
mail-client/evolution:profile - Build support for profiling Evolution for development purposes
mail-client/mail-notification:gmail - Enable Gmail mailbox checking
mail-client/mail-notification:mh - Enable MH mailbox checking
mail-client/mail-notification:pop - Enable support for pop
mail-client/mail-notification:sylpheed - Enable support for MH mailboxes used by mail-client/sylpheed
mail-client/mutt:gpg - Enable support for app-crypt/gpgme
mail-client/mutt:pop - Enable support for pop
mail-client/mutt:sidebar - Use the vanilla tree + sidebar patch
mail-client/mutt:smime - Enable support for smime
mail-client/mutt:smtp - Enable support for smtp
mail-client/mutt:tokyocabinet - Enable tokyocabinet database backend for header caching
mail-client/nail:kerberos -  If network is enabled, this adds support for GSSAPI login on IMAP through virtual/kerberos. 
mail-client/nail:net -  Enable support for network protocols (POP, IMAP and SMTP). If you only need to send mail with the local Transport Agent, disabling this will get you support for only /usr/sbin/sendmail call. 
mail-client/nail:ssl -  If network is enabled, this adds support for S/MIME and SSL/TLS-powered protocols through dev-libs/openssl. 
mail-client/pine:largeterminal - Add support for large terminals by doubling the size of pine's internal display buffer
mail-client/pine:passfile - Adds support for caching IMAP passwords into a file between sessions
mail-client/squirrelmail:filter - Enable mail-filter/amavisd-new filtering
mail-client/thunderbird:custom-optimization - Enable user CFLAGS
mail-client/thunderbird:lightning - Enable calendar support
mail-client/thunderbird:mozdom - Enable Mozilla's DOM inspector
mail-client/thunderbird:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
mail-filter/amavisd-new:courier - Add courier support
mail-filter/amavisd-new:dkim - Add DomainKeys Identified Mail support
mail-filter/amavisd-new:qmail - Add qmail support
mail-filter/amavisd-new:razor - Add support for mail-filter/razor
mail-filter/amavisd-new:spamassassin - Add support for mail-filter/spamassassin
mail-filter/ask:procmail - Adds support for mail-filter/procmail
mail-filter/assp:spf - Adds support for Sender Policy Framework
mail-filter/assp:srs - Adds support for Sender Rewriting Scheme
mail-filter/bogofilter:tokyocabinet - Enable Tokyo Cabinet database support
mail-filter/clamassassin:clamd - Use the app-antivirus/clamav daemon for virus checking
mail-filter/clamassassin:subject-rewrite - Adds support for subject rewriting
mail-filter/dcc:rrdtool - Enable net-analyzer/rrdtool interface scripts
mail-filter/dkim-milter:diffheaders - On verification failure, compare the original and the received headers to look for possible munging
mail-filter/dovecot-antispam:crm114 - Build CRM114 backend
mail-filter/dovecot-antispam:dspam - Build mail-filter/dspam backend
mail-filter/dovecot-antispam:mailtrain - Build mailtrain backend
mail-filter/dovecot-antispam:signature-log - Build signature-log backend
mail-filter/dovecot-antispam:spool2dir - Build spool directory backend
mail-filter/dspam:daemon -  Enable support for DSPAM to run in --daemon mode 
mail-filter/dspam:debug -  Enable debugging support (don't enable this unless something needs testing!) 
mail-filter/dspam:debug-bnr -  Activates debugging output for Bayesian Noise Reduction 
mail-filter/dspam:debug-verbose -  Cause DSPAM produce verbose debug output and write them into LOGDIR/dspam.debug file. Never enable this for production builds! 
mail-filter/dspam:large-domain -  Builds for large domain rather than for domain scale 
mail-filter/dspam:user-homedirs -  uild with user homedir support 
mail-filter/dspam:virtual-users -  Build with virtual-users support 
mail-filter/libmilter:poll - Use poll instead of select
mail-filter/maildrop:authlib - Add courier-authlib support
mail-filter/mimedefang:poll - Use poll instead of select
mail-filter/opendkim:asyncdns - Use inbuilt asynchronous DNS library for queries
mail-filter/opendkim:db - Include features like stats, querycache, popauth, report intervals and bodylengthdb that include berkdb
mail-filter/opendkim:ldap - Enable openldap as a dataset facilitator or keys, determining domains to sign for, and any other dataset that opendkim supports.
mail-filter/opendkim:lua - Enables control over signature verification, filtering and policy to be controlled by user defined lua scripts.
mail-filter/opendkim:opendbx - Use opendbx backend to facilitate dataset driven OpenDKIM configuration options like stats, bodylengthdb, etc. against a wide variety of database types
mail-filter/opendkim:sasl - Used to authenticate to a LDAP server in various ways if required.
mail-filter/opendkim:unbound - Use the unbound dnssec library to perform DKIM DNS queries.
mail-filter/postgrey:targrey - Enables the targrey patch
mail-filter/qmail-scanner:spamassassin - Build faster mail-filter/spamassassin checks into qmail-scanner
mail-filter/spamassassin:qmail - Build qmail functionality and docs
mail-filter/spamassassin:tools - Enables tools for spamassassin
mail-filter/spamassassin-fuzzyocr:amavis - Enable support for mail-filter/amavisd-new
mail-filter/spamassassin-fuzzyocr:gocr - Enable support for the gocr OCR engine
mail-filter/spamassassin-fuzzyocr:logrotate - Install support files for app-admin/logrotate
mail-filter/spamassassin-fuzzyocr:ocrad - Enable support for the ocrad OCR engine
mail-filter/spamassassin-fuzzyocr:tesseract - Enable support for the tesseract OCR engine
mail-filter/spamdyke:tls - Enables TLS protocol for spamdyke
mail-filter/zdkimfilter:debug -  Log process and signal information. Also leave the child process running for gdb examination. 
mail-filter/zdkimfilter:mysql -  MySQL client based statistics based storage. 
mail-filter/zdkimfilter:opendbx -  An alternate statistics based storage engine. 
mail-mta/courier:fax - Enables fax support in the courier mail server
mail-mta/courier:norewrite - Prevents courier mail server from mangling virtual user addresses when sending
mail-mta/courier:web - Enable the web interface
mail-mta/courier:webmail - Enable the webmail interface
mail-mta/exim:dcc - Adds support for Distributed Checksum Clearinghouse (DCC)
mail-mta/exim:dkim - Adds support for DomainKeys Identified Mail (DKIM)
mail-mta/exim:dnsdb - Adds support for a DNS search for a record whose domain name is the supplied query
mail-mta/exim:dovecot-sasl - Adds support for Dovecot's authentication
mail-mta/exim:dsn - Adds support for Delivery Status Notifications (DSN)
mail-mta/exim:exiscan-acl - Patch providing support for content scanning
mail-mta/exim:lmtp - Adds support for lmtp
mail-mta/exim:mbx - Adds support for UW's mbx format
mail-mta/exim:spf - Adds support for Sender Policy Framework
mail-mta/exim:srs - Adds support for Sender Rewriting Scheme
mail-mta/msmtp:mta - Enable this to install as system-wide MTA
mail-mta/netqmail:authcram - Enable AUTHCRAM support
mail-mta/netqmail:gencertdaily - Generate SSL certificates daily instead of hourly
mail-mta/netqmail:highvolume - Prepare netqmail for high volume servers
mail-mta/netqmail:noauthcram - If you do NOT want AUTHCRAM to be available
mail-mta/postfix:dovecot-sasl - Enable net-mail/dovecot protocol version 1 (server only) SASL implementation
mail-mta/postfix:vda - Adds support for virtual delivery agent quota enforcing
mail-mta/qmail-ldap:cluster - Enable this if you want to have cluster support in qmail-ldap
mail-mta/qmail-ldap:gencertdaily - Generate SSL certificates daily instead of hourly
mail-mta/qmail-ldap:highvolume - Prepare qmail for high volume servers
mail-mta/qmail-ldap:rfc2307 - Add support for RFC2307 compliant uid/gid attributes
mail-mta/qmail-ldap:rfc822 - Add support for RFC822 compliant mail attributes
mail-mta/qpsmtpd:async - Add deps + support for asynchronous mail reception/processing as well as preforked daemon
mail-mta/qpsmtpd:postfix - create user with permissions for proper postfix interaction
mail-mta/ssmtp:maxsysuid - Allow to define a MinUserId
mail-mta/ssmtp:md5sum - Enables MD5 summing for ssmtp
media-fonts/culmus:ancient - Install ancient semitic scripts
media-fonts/culmus:fancy - Install fancy fonts
media-fonts/culmus:fontforge - Use media-gfx/fontforge to build fonts from source
media-fonts/culmus:taamey - Install taamey fonts
media-fonts/culmus-ancient:fontforge - Use media-gfx/fontforge to build fonts from source
media-fonts/dejavu:fontforge - Use media-gfx/fontforge to build fonts from source
media-fonts/intlfonts:bdf - Installs BDF fonts in addition to PCF
media-fonts/liberation-fonts:fontforge - Use media-gfx/fontforge to build fonts from source
media-fonts/mplus-outline-fonts:ipafont - Generates new fonts merged with media-fonts/ja-ipafonts
media-fonts/sil-charis:compact - Use more compactly spaced font
media-fonts/terminus-font:a-like-o - Changes view of letter 'a' - a looks like o (see homepage)
media-fonts/terminus-font:bolddiag - Boldified diagonal parts of '4', 'k', 'x' and some other chars
media-fonts/terminus-font:pcf - Install Portable Compiled Font (PCF) (required for X11)
media-fonts/terminus-font:psf - Install PC Screen Font (PSF) with unicode data (for linux console)
media-fonts/terminus-font:quote - Changes view of quotes: symmetric ` and ' instead of asymmetric one (see homepage)
media-fonts/terminus-font:raw-font-data - Install RAW font data which should be compatible with most UNIX systems (you don't need this on linux)
media-fonts/terminus-font:ru-dv - Changes view of Russian letters 'de' and 've' (see homepage)
media-fonts/terminus-font:ru-g - Changes view of Russian letter 'ge' (see homepage)
media-fonts/terminus-font:ru-i - Changes view of Russian letter 'i' - not like Latin u, but like "mirrored" N (see homepage)
media-fonts/terminus-font:ru-k - Changes view of Russian letter 'k' (see homepage)
media-fonts/terminus-font:width - Wider versions of some font elements
media-gfx/album:plugins - Install optional plugins
media-gfx/album:themes - Install optional themes
media-gfx/asymptote:boehm-gc -  Enables using the Boehm-Demers-Weiser conservative garbage collector 
media-gfx/asymptote:sigsegv -  Enables using dev-libs/libsigsegv 
media-gfx/blender:blender-game -  Adds game engine support to blender 
media-gfx/blender:player -  Enable blender player 
media-gfx/blender:verse -  Adds verse clustering features to blender 
media-gfx/comix:rar -  Pulls app-arch/unrar for rar file support 
media-gfx/digikam:addressbook - Add support for kdepim
media-gfx/digikam:geolocation - Add support for marble
media-gfx/digikam:lensfun - Enable support for lens-correnction library
media-gfx/digikam:themedesigner - Build the digikam theme designer
media-gfx/digikam:thumbnails - Enable thumbnails database support
media-gfx/digikam:video - Pull in mplayerthumbs to enable video thumbnails
media-gfx/enblend:gpu - GPU support for Enblend
media-gfx/enblend:image-cache - allow for processing of large images
media-gfx/exact-image:swig - Adds Swig support dev-lang/swig
media-gfx/exiv2:contrib -  Build additional contrib components 
media-gfx/f-spot:beagle - Enable app-misc/beagle support for searches
media-gfx/f-spot:flickr - Enable building of the Flickr exported.
media-gfx/fontforge:cjk - Controls whether fontforge understands the gb12345 encoding and installs cidmap package to edit CID-keyed fonts
media-gfx/fontforge:pango - Enable pango font rendering
media-gfx/fontforge:pasteafter - Controls whether fontforge has a paste after command (Useful for making words?). This is kind of fun, but it isn't useful for normal fonts.
media-gfx/fontforge:tilepath - Controls whether fontforge has a tile path command (a variant of expand stroke) This is useful for very decorative fonts, most people won't want it.
media-gfx/fontforge:truetype-debugger - Enable truetype debugger in fontforge
media-gfx/fontforge:type3 - Build in support for type3/svg fonts containing multilayered drawing with strokes, fills, images, etc. Type3 fonts are only supported by postscript printers (not by most windowing displays). They are capable of more exotic images than normal fonts but require much more effort to support.
media-gfx/fotowall:webcam - Enable webcam support
media-gfx/freewrl:glew - Enable glew extensions
media-gfx/freewrl:libeai - Build EAI C library
media-gfx/freewrl:spidermonkey - Use spidermonkey instead of Firefox
media-gfx/gimp:smp -  Enable support for multiprocessors 
media-gfx/gimp:webkit -  Enable the webkit rendering engine 
media-gfx/graphicsmagick:fpx - Enable FlashPix support with media-libs/libfpx
media-gfx/graphicsmagick:modules - Compile graphicsmagick with dynamically loadable modules
media-gfx/graphicsmagick:q16 - Set storage quantum size to 16 (~2*memory)
media-gfx/graphicsmagick:q32 - Set storage quantum size to 32 (~5*memory)
media-gfx/graphviz:lasi -  Enables PostScript output via media-libs/lasi library 
media-gfx/gthumb:http - Enable webservice integration through net-libs/libsoup
media-gfx/gthumb:iptc - Add support for IPTC metadata
media-gfx/gthumb:slideshow - Enable slideshow plugin
media-gfx/hugin:sift - automatically align images with media-gfx/autopano-sift or media-gfx/autopano-sift-C
media-gfx/imagemagick:autotrace -  use media-gfx/autotrace to convert bitmaps into vector graphics 
media-gfx/imagemagick:corefonts -  pull in media-fonts/corefonts, which is required for some commands 
media-gfx/imagemagick:fpx -  enable media-libs/libfpx support 
media-gfx/imagemagick:gs -  enable ghostscript support 
media-gfx/imagemagick:hdri -  enable High Dynamic Range Images formats 
media-gfx/imagemagick:lqr -  enable experimental liquid rescale support 
media-gfx/imagemagick:q32 -  set quantum depth to 32 
media-gfx/imagemagick:q8 -  set quantum depth to 8 
media-gfx/inkscape:dia -  pull in app-office/dia for dia import extension 
media-gfx/inkscape:gs -  enables support for the PostScript import extension 
media-gfx/inkscape:inkjar -  enables support for OpenOffice.org SVG jar files 
media-gfx/jpeg2ps:metric -  Default to A4 paper size 
media-gfx/k3d:3ds - Enable support for 3D Studio models
media-gfx/k3d:cuda - Use nvidia cuda toolkit for speeding up computations
media-gfx/k3d:gts - Add Support for the GNU Triangulated Surface Library sci-libs/gts
media-gfx/kphotoalbum:geolocation - Add support for kde-base/marble
media-gfx/kphotoalbum:kipi - Support for the KDE Image Plugin Interface
media-gfx/nip2:goffice - use x11-libs/goffice to show plots
media-gfx/openclipart:gzip - Compresses clip art using gzip
media-gfx/potrace:metric -  default to a4 paper size and metric measurement 
media-gfx/povray:mkl - Enable support for Intel Vector Math Library, part of sci-libs/mkl
media-gfx/pstoedit:emf - Enable media-libs/libemf support
media-gfx/pstoedit:flash - Enable media-libs/ming SWF support
media-gfx/scantailor:dewarping - Enable experimental dewarping support
media-gfx/splashutils:fbcondecor -  Support for the fbcondecor kernel patch. 
media-gfx/ufraw:contrast -  enable contrast setting option 
media-gfx/ufraw:fits -  Enable support for the FITS image format through sci-libs/cfitsio 
media-gfx/ufraw:hotpixels -  enable hot pixel elimination 
media-gfx/ufraw:lensfun -  enable the lensfun lens-correction library 
media-gfx/ufraw:timezone -  enable DST correction for file timestamps 
media-gfx/yafaray:blender - install media-gfx/blender scripts
media-libs/a52dec:djbfft - Prefer D.J. Bernstein's library for fourier transforms
media-libs/allegro:vga - Enables the VGA graphics driver
media-libs/alsa-lib:alisp - Enable support for ALISP (ALSA LISP) interpreter for advanced features.
media-libs/cal3d:16bit-indices - Enables use of 16bit indices
media-libs/clutter:gtk - Use gdk-pixbuf from x11-libs/gtk+ as image rendering backend
media-libs/clutter:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/clutter-gst:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/clutter-gtk:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/coin:simage - Texture loading via media-libs/simage library
media-libs/devil:allegro - Add support for Allegro
media-libs/edje:cache - Enable caching
media-libs/esdl:image - Enable image support
media-libs/evas:cache - Enable experimental caching to speed up rendering
media-libs/evas:eet - Support dev-libs/eet
media-libs/evas:gles - Enable gles falvor of gl instead of standard
media-libs/faad2:digitalradio - Digital Radio Mondiale (warning: disables other decoders)
media-libs/freeglut:mpx -  Enable support for multi-pointer-X. One pointer for each pointer device. 
media-libs/freetype:auto-hinter - Use the unpatented auto-hinter instead of the (recommended) TrueType bytecode interpreter
media-libs/freetype:fontforge - Install internal headers required for TrueType debugger in media-gfx/fontforge (built with USE=truetype-debugger)
media-libs/freetype:kpathsea - Enable TeX support (ttf2pk and ttf2pfb)
media-libs/freetype:utils - Install utilities and examples from ft2demos
media-libs/freeverb3:audacious - Build Audacious plugin
media-libs/freeverb3:forcefpu - Disable assembly code
media-libs/freeverb3:plugdouble - Build plugins in double precision mode (default is float)
media-libs/freeverb3:sse3 - Enable SSE3 support
media-libs/freeverb3:sse4 - Enable SSE4 support
media-libs/giflib:rle - Build converters for RLE format (utah raster toolkit)
media-libs/glide-v3:voodoo1 - Support 3DFX Voodoo1 video cards
media-libs/glide-v3:voodoo2 - Support 3DFX Voodoo2 video cards
media-libs/glide-v3:voodoo5 - Support 3DFX Voodoo4 and Voodoo5 video cards
media-libs/gst-plugins-base:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/gst-plugins-base:orc - Use dev-lang/orc for runtime optimisations
media-libs/gstreamer:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/imlib:deprecated - Enable deprecated GTK+-1.2 support
media-libs/libass:enca - Enables support for charset discovery and conversion.
media-libs/libbluray:aacs - Add support for decryption of AACS
media-libs/libcanberra:alsa - Enables ALSA sound driver.
media-libs/libcanberra:gstreamer - Enables gstreamer sound driver. Not useful when alsa or pulseaudio is available.
media-libs/libcanberra:gtk - Enables building of gtk+ helper library, gtk+ runtime sound effects and the canberra-gtk-play utility. To enable the gtk+ sound effects add canberra-gtk-module to the colon separated list of modules in the GTK_MODULES environment variable.
media-libs/libcanberra:pulseaudio - Enables PulseAudio sound driver that should be able to support positional event sounds. This is the preferred choice for best sound events experience and picked by default if compiled in and possible to use at runtime.
media-libs/libcanberra:sound - Install x11-themes/sound-theme-freedesktop to get sounds on Gnome and Xfce.
media-libs/libcanberra:tdb - Enables Trivial Database support
media-libs/libchamplain:html - Install gtk-doc html version for this package
media-libs/libchamplain:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/libggi:vis - Enables sparc vis support for libggi
media-libs/libgpod:gtk - Enables ArtWorkDB support (including Photos and album covers)
media-libs/libgpod:iphone - Enables support for the iPhone and iPod touch
media-libs/libmediainfo:libmms - Support for Microsoft Media Server (MMS) streams via libmms
media-libs/libmikmod:raw - Enable raw file writer plug-in
media-libs/libmp4v2:utils - Install command-line utilities
media-libs/libquicktime:schroedinger - Enable Dirac video support (an advanced royalty-free video compression format) via libschroedinger (high-speed implementation in C of the Dirac codec).
media-libs/libsdl:audio - Control audio support (disable at your own risk)
media-libs/libsdl:joystick - Control joystick support (disable at your own risk)
media-libs/libsdl:ps3 - Build the PS3 video driver
media-libs/libsdl:tslib - Build with tslib support for touchscreen devices
media-libs/libsdl:video - Control video support (disable at your own risk)
media-libs/libvpx:postproc - Enable additional post processing filters
media-libs/libvpx:sse3 - Enable optimization for SSE3 capable chips
media-libs/libvpx:ssse3 - faster floating point optimization for SSSE3 capable chips (Intel Core 2 and later chips)
media-libs/mediastreamer:ilbc - Use of iLBC (RFC3951) codec plugin
media-libs/mediastreamer:video - Enable video support
media-libs/memphis:introspection - Use dev-libs/gobject-introspection for introspection
media-libs/memphis:vala - Add support for Vala
media-libs/mesa:classic - Build drivers based on the classic architecture.
media-libs/mesa:gallium - Build drivers based on Gallium3D, the new architecture for 3D graphics drivers.
media-libs/mesa:gles - Enable GLES support for Gallium3D.
media-libs/mesa:llvm - Enable LLVM backend for Gallium3D.
media-libs/mesa:pic - disable optimized assembly code that is not PIC friendly
media-libs/mlt:compressed-lumas - Compress the luma files in png.
media-libs/mlt:frei0r - Build the module for media-plugins/frei0r-plugins
media-libs/mlt:lua - Build SWIG bindings for Lua
media-libs/mlt:melt - Build the melt commandline tool
media-libs/mlt:python - Build SWIG bindings for Python
media-libs/mlt:ruby - Build SWIG bindings for Ruby
media-libs/mlt:vdpau - Build with vdpau support
media-libs/netpbm:rle - Build converters for the RLE format (utah raster toolkit)
media-libs/opencv:deprecated - Enable deprecated (old) python support
media-libs/opencv:ipp - Enable Intel Integrated Primitive support
media-libs/opencv:octave - Enable octave support
media-libs/opencv:sse3 - Enable optimization for SSE3 capable chips
media-libs/opencv:ssse3 - faster floating point optimization for SSSE3 capable chips (Intel Core 2 and later chips)
media-libs/openjpeg:tools - Installs tools (j2k_to_image and image_to_j2k)
media-libs/raptor:json - Enable support for JSON parsing
media-libs/sdif:ftruncate - Enables usage of ftruncate v. truncate
media-libs/sdl-mixer:midi - basic support for MIDI files
media-libs/sdl-mixer:wav - support WAVE files
media-libs/sdl-sound:physfs - Enable physfs support
media-libs/sge:image - enable sdl-image support
media-libs/silgraphite:pango - Enables the pango-graphite pango module.
media-libs/spandsp:fixed-point - Enable fixed point support
media-libs/spandsp:sse3 - Enable SSE3 support
media-libs/spandsp:sse4 - Enable SSE4 support
media-libs/spandsp:sse4a - Enable SSE4a support
media-libs/spandsp:sse5 - Enable SSE5 support
media-libs/svgalib:kernel-helper - Build the helper kernel module
media-libs/swfdec:alsa - Use ALSA for audio output
media-libs/swfdec:doc - Build documentation
media-libs/swfdec:ffmpeg - Use media-plugins/gst-plugins-ffmpeg to enable Flash video support. Necessary if you want to use sites like youtube
media-libs/swfdec:gstreamer - Enable media-libs/gstreamer to support various media input formats. i.e. audio (mp3) and video (flv)
media-libs/swfdec:gtk - Enable GTK+ convenience library while is necessary for all GTK+ apps using swfdec (gnome-extra/swfdec-gnome and www-plugins/swfdec-mozilla)
media-libs/swfdec:pulseaudio - Use media-sound/pulseaudio for audio output
media-libs/taglib:asf - Provide support for Microsoft's 'advanced systems format' media container.
media-libs/urt:gs - Add support for postscript
media-libs/win32codecs:real - Installs the real video codecs
media-libs/x264:pic - disable optimized assembly code that is not PIC friendly
media-libs/xine-lib:dxr3 -  Enable support for DXR3 mpeg acceleration cards. 
media-libs/xine-lib:flac -  Build the media-libs/flac based FLAC demuxer and decoder. This flag is not needed for playing FLAC content, neither standalone nor in Ogg container (OggFLAC), but might have better support for exotic features like 24-bit samples or 96kHz sample rates. 
media-libs/xine-lib:gnome -  Build the gnome-base/gnome-vfs based input plugin. This plugin is used to access any resource that can be accessed through Nautilus's (and others') URLs. 
media-libs/xine-lib:gtk -  Build the gdkpixbuf-based image decoder plugin. 
media-libs/xine-lib:imagemagick -  Build the ImageMagick-based image decoder plugin. 
media-libs/xine-lib:mad -  Build the media-libs/libmad based mp3 decoder. This mp3 decoder has superior support compared to the one coming from FFmpeg that is used as a fallback. If you experience any bad behaviour with mp3 files (skipping, distorted sound) make sure you enabled this USE flag. 
media-libs/xine-lib:mmap -  Use mmap() function while reading file from local disks. Using mmap() will use more virtual memory space, but leaves to the Kernel the task of caching the file's data. mmap() access should be faster, but might misbehave if the device where the file resides in is removed during playback. 
media-libs/xine-lib:real -  Enable support for loading and using RealPlayer binary codecs on x86 and amd64 Linux. Enabling this USE flag might make the package non-redistributable in binary form. 
media-libs/xine-lib:truetype -  Use media-libs/freetype for font rendering and media-libs/fontconfig for font discovery. Enabling this USE flag will allow OSD (such as subtitles) to use more advanced font and to more easily select which font to use. The support for TrueType fonts in xine-lib is still experimental, and might not be as good looking as the bitmap fonts used with this USE flag disabled. 
media-libs/xine-lib:vidix -  Enable support for vidix video output. 
media-libs/xine-lib:vis -  Adds support for SIMD optimizations for UltraSPARC processors. 
media-libs/xine-lib:win32codecs -  Enable support for loading and using Windows 32-bit binary codecs on x86 Linux and FreeBSD. Enabling this USE flag might make the package non-redistributable in binary form. 
media-libs/xine-lib:xvmc -  Enable support for XVideo Motion Compensation (accelerated mpeg playback). 
media-libs/xvid:pic - disable optimized assembly code that is not PIC friendly
media-plugins/audacious-plugins:adplug - Build with AdPlug (Adlib sound card emulation) support
media-plugins/audacious-plugins:bs2b - Enable Bauer Bauer stereophonic-to-binaural headphone filter
media-plugins/audacious-plugins:cue - Support CUE sheets using the libcue library
media-plugins/audacious-plugins:fluidsynth - Support FluidSynth as MIDI synth backend
media-plugins/audacious-plugins:icecast - Support for Icecast2 streaming
media-plugins/audacious-plugins:midi - Build with amidi-plug (MIDI synth) support
media-plugins/audacious-plugins:projectm - Build with ProjectM visualization
media-plugins/audacious-plugins:scrobbler - Build with scrobbler/LastFM submission support
media-plugins/audacious-plugins:sid - Build with SID (Commodore 64 Audio) support
media-plugins/banshee-community-extensions:lirc - Enable the remote control plugin (uses app-misc/lirc)
media-plugins/banshee-community-extensions:lyrics - Enable support for automatically fetching lyrics
media-plugins/banshee-community-extensions:mirage - Enable the Mirage plugin which automatically, and intelligently generates playlists for you
media-plugins/banshee-community-extensions:telepathy - Enables the Telepathy plugin which lets you to share and stream music with IM buddies
media-plugins/frei0r-plugins:facedetect - Enables building of facedetect plugin, which depends on media-libs/opencv 
media-plugins/frei0r-plugins:scale0tilt - Enables building of scale0tilt and vectorscope plugins, which depend on media-libs/gavl 
media-plugins/gkrellmpc:threads - Use separate thread to init connection (unsafe)
media-plugins/gst-plugins-meta:mythtv - Support for retrieval from media-tv/mythtv backend
media-plugins/kipi-plugins:expoblending - Build the expoblending plugin, which requires media-gfx/hugin
media-plugins/kipi-plugins:mjpeg - Add mjpeg suppport
media-plugins/kipi-plugins:redeyes - Add redeyes removal suppport
media-plugins/mythmusic:libvisual - Enables media-libs/libvisual support for effects
media-plugins/mythvideo:jamu - Use and configure the Just Another Metadata Utility by default
media-plugins/mythzoneminder:minimal - Don't build the mythtv side of this plugin, only the part that communicates with zoneminder. 
media-plugins/vdr-burn:projectx - Enables support for media-video/projectx
media-plugins/vdr-dvdconvert:projectx - Enable support for media-video/projectx
media-plugins/vdr-epgsearch:tre - Add support for unlimited fuzzy searching with help of dev-libs/tre library
media-plugins/vdr-graphtft:graphtft-fe - Install external x11 remote frontend
media-plugins/vdr-graphtft:theme_avp - graphTFT Alien vs. Predato theme
media-plugins/vdr-graphtft:theme_deepblue - graphTFT default theme
media-plugins/vdr-graphtft:theme_deeppurple - graphTFT Deep Purple theme
media-plugins/vdr-graphtft:theme_poetter - graphTFT Poetter theme
media-plugins/vdr-graphtft:touchscreen - Enable Touchscreen support
media-plugins/vdr-music:4mb-mod - Enables support for modded FF-Card to 4MB ram or softdecoder
media-plugins/vdr-music:ff-card - Enables scrollmode on FF-Card
media-plugins/vdr-music:graphtft - Enable support for media-plugins/vdr-graphtft
media-plugins/vdr-pvr350:yaepg - Enables full support for the output format of media-plugins/vdr-yaepg
media-plugins/vdr-softdevice:mmxext - enables MMXExt support
media-plugins/vdr-streamdev:client -  Compile the VDR plugin vdr-streamdev-client that acts like a dvb-budget card 
media-plugins/vdr-streamdev:server -  Compile the VDR plugin vdr-streamdev-server that allows remote systems to access the DVB cards used for the local VDR 
media-plugins/vdr-text2skin:direct_blit - not buffer picture, faster, but only for modified skins
media-plugins/vdr-weatherng:dxr3 - enables lower osd color depth for dxr3 cards
media-plugins/vdr-xineliboutput:libextractor - Use media-libs/libextract to gather files' metadata in media-player
media-plugins/vdr-xineliboutput:vdpau - Enables VDPAU support (requires nVidia video cards) to offload MPEG2/MPEG4/VC1/WMV CPU processing to video card
media-plugins/vdr-xineliboutput:vdr - Compile the vdr output plugin to use local or remote xine as output
media-plugins/vdr-xineliboutput:xine - Compile the xine input plugin for displaying vdr video and OSD
media-radio/fldigi:hamlib - Enables support by the Hamlib amateur radio rig control library to get/set frequency and mode of the ham radio in use
media-radio/tucnak2:ftdi - Enable support for FTDI USB chips
media-radio/tucnak2:hamlib - Enables support by the Hamlib amateur radio rig control library to get/set frequency and mode of the ham radio
media-radio/unixcw:ncurses - Enables building the curses based morse code tutor program 'cwcp'.
media-radio/xastir:festival - Enable text to speech synthesizer
media-radio/xastir:gdal - Support for some further map formats
media-radio/xastir:geotiff - Install geotiff support. Allows using USGS DRG topo maps or other types of geotiff mapes/images
media-radio/xastir:graphicsmagick - Use graphicsmagick instead imagemagick for rendering
media-sound/abcde:id3 - Support ID3, ID3v2 tagging of audio files
media-sound/abcde:normalize - Add support for normalizing audio file volume levels
media-sound/abcde:replaygain - Support for Replay Gain metadata, for relative volume adjustment
media-sound/alsaplayer:id3tag - Enables ID3 tagging with id3tag library
media-sound/amarok:daap -  Enable the scripts for music sharing through DAAP. This flag adds dependencies on www-servers/mongrel to allow sharing of the Amarok music collection through DAAP protocol. Please note that turning this flag off has no effect on DAAP browsing. 
media-sound/amarok:embedded -  Use libmysqld, MySQL embedded server library. Try disabling this if you encounter -PIC related in amarok, it will make amarok rely only on standalone MySQL server. 
media-sound/amarok:lastfm - Enable Last.fm streaming services support through media-libs/liblastfm
media-sound/amarok:mp3tunes - Enable mp3tunes integration
media-sound/amarok:player - Build the player
media-sound/amarok:utils - Build the utils - old media-sound/amarok-utils
media-sound/aqualung:ifp - Enable support for iRiver iFP portable audio players
media-sound/aqualung:lua - Enable support for programmable title formatting with dev-lang/lua
media-sound/aqualung:mac - Enable support for decoding Monkey's Audio files
media-sound/aqualung:podcast - Enable podcast support
media-sound/aqualung:systray - Enable system tray support
media-sound/ardour:lv2 - Add support for Ladspa V2
media-sound/ario:audioscrobbler - Enable song tracking via last.fm
media-sound/ario:idle - Enable experimental support for MPD's idle command to reduce bandwidth and cpu usage, requires MPD 0.14
media-sound/audacious:chardet - Try to handle non-UTF8 chinese/japanese/korean ID3 tags
media-sound/audacity:id3tag - Enables ID3 tagging with id3tag library
media-sound/audacity:midi - Enables MIDI support
media-sound/audacity:soundtouch - Enables soundtouch library support
media-sound/audacity:twolame - Enables twolame support (MPEG Audio Layer 2 encoder)
media-sound/audacity:vamp - Enables vamp plugins support (Audio analysing plugins)
media-sound/banshee:boo - Use external Boo instead of the bundled one
media-sound/banshee:cdda - Build with audio CD support
media-sound/banshee:daap - Build with Daap support
media-sound/banshee:karma - Build with karma support
media-sound/banshee:podcast - Build with podcasting support
media-sound/banshee:web - Enable support for plugins that access web-based services such as Amazon and wikipedia (requires net-libs/webkit-gtk)
media-sound/banshee:wikipedia - Enable the Wikipedia context pane (require net-libs/webkit-gtk)
media-sound/banshee:youtube - Enable the Youtube plugin
media-sound/clementine:iphone - Enable support for iPod Touch, iPhone, iPad
media-sound/clementine:projectm - Build with ProjectM visualization
media-sound/clementine:wiimote - Enable support for Wii remote
media-sound/cmus:pidgin - install support script for net-im/pidgin
media-sound/cmus:wma - add support for Windows Media Audio
media-sound/darkice:twolame - Build with twolame support
media-sound/decibel-audio-player:gnome - Adds Gnome media keys support, so you can control Decibel using hotkeys. 
media-sound/decibel-audio-player:gnome-keyring - Adds support for storing your Last.fm password using gnome-keyring.
media-sound/dir2ogg:mac - Add support for decoding Monkey's Audio files
media-sound/dir2ogg:wma - Add support for wma files through mplayer
media-sound/fapg:xspf - Enable support for saving XSPF playlists.
media-sound/freewheeling:fluidsynth - compile with support for fluidsynth
media-sound/gejengel:audioscrobbler - Enable track submission on last.fm
media-sound/gimmix:cover - Enable cover art fetching
media-sound/gimmix:lyrics - Enable lyric fetching
media-sound/gmpc:xspf - Enable support for reading and saving XSPF playlists
media-sound/gmusicbrowser:webkit - Enables gtk WebKit support
media-sound/gpodder:webkit - Enable the webkit rendering engine for HTML episode shownotes
media-sound/herrie:http - Enable http streaming
media-sound/herrie:xspf - Enable support for reading and saving XSPF playlists
media-sound/hydrogen:archive - Use libarchive instead of libtar
media-sound/jack-audio-connection-kit:coreaudio - Build the CoreAudio driver on Mac OS X systems
media-sound/jack-audio-connection-kit:cpudetection - Enables runtime cpudetection
media-sound/jack-audio-connection-kit:netjack - Build with support for Realtime Audio Transport over generic IP
media-sound/kwave:phonon - Enable media-sound/phonon support
media-sound/lame:mp3rtp - Build the mp3-to-RTP streaming utility. **UNSUPPORTED**
media-sound/listen:libsexy - Enable libsexy support
media-sound/listen:webkit - Enable webkit rendering engine instead of mozembed
media-sound/lmms:fluidsynth - Enables Fluidsynth MIDI software synthesis plugin.
media-sound/lmms:stk - Enables STK Mallet plugin.
media-sound/lmms:vst - Enables the VeSTige plugin to run VST plugins through Wine.
media-sound/mangler:celt - High quality, low delay audio codec
media-sound/mangler:espeak - Text to speach engine
media-sound/mangler:g15 - Logitech g15 lcd support
media-sound/mixxx:hifieq - Enable hifi equalizer support
media-sound/mixxx:shout - Enable shoutcast support
media-sound/mixxx:tonal - Enable tonal analysis support
media-sound/mixxx:vinylcontrol - Enable vinylcontrol feature
media-sound/moc:sid - Build with SID (Commodore 64 Audio) support
media-sound/mp3blaster:sid - Build with SID (Commodore 64 Audio) support
media-sound/mp3splt-gtk:audacious - Include media-sound/audacious support
media-sound/mpd:cdio - Use libcdio for ISO9660 parsing support
media-sound/mpd:cue - Support CUE Sheet Parser Library
media-sound/mpd:curl - Support for web stream listening
media-sound/mpd:fifo - Support writing audio to a FIFO
media-sound/mpd:fluidsynth - Enables Fluidsynth MIDI software synthesis
media-sound/mpd:id3 - Support for ID3 tags
media-sound/mpd:lame - Support for MP3 streaming via Icecast2
media-sound/mpd:lastfmradio - Support listening to last.fm radio stations
media-sound/mpd:libmms - Support for Microsoft Media Server (MMS) streams via libmms
media-sound/mpd:mpg123 - Enable support for mp3 decoding over media-sound/mpg123.
media-sound/mpd:network - Enables network streaming support
media-sound/mpd:pipe - Support writing audio to a pipe
media-sound/mpd:sid - Build with SID (Commodore 64 Audio) support
media-sound/mpd:wildmidi - Enable MIDI support via wildmidi
media-sound/mpd:zip - Support for ZIP files
media-sound/mpfc:wav - Enable wav audio codec support
media-sound/mpg123:3dnowext - Enable 3dnowext cpu instructions
media-sound/mumble:g15 - Enable support for the Logitech G15 LCD (and compatible devices).
media-sound/mumble:speech - Enable text-to-speech support in Mumble.
media-sound/murmur:ice - Use dev-cpp/Ice to enable remote control capabilities.
media-sound/ncmpc:artist-screen - Enable artist screen
media-sound/ncmpc:colors - Enable color support
media-sound/ncmpc:help-screen - Enable the help screen
media-sound/ncmpc:key-screen - Enable key editor screen
media-sound/ncmpc:lyrics-screen - Enable lyrics screen
media-sound/ncmpc:mouse - Enable curses getmouse support
media-sound/ncmpc:search-screen - Enable search screen
media-sound/ncmpc:song-screen - Enable song viewer screen
media-sound/ncmpcpp:clock - Enable clock screen
media-sound/ncmpcpp:fftw - Build the visualizer plugin that pulls in sci-libs/fftw
media-sound/ncmpcpp:outputs - Enable outputs screen
media-sound/ncmpcpp:visualizer - Enable visualizer screen with sound wave/frequency spectrum modes
media-sound/picard:coverart - Install plugin for direct coverart dowload
media-sound/pms:regex - Enable regular expression searches using dev-libs/boost
media-sound/podcatcher:bittorrent - Enable support for bittorrent downloads
media-sound/puddletag:cover -  Enables editing of FLAC cover art
media-sound/puddletag:quodlibet - Enables editing a QuodLibet library
media-sound/pulseaudio:X -  Build the X11 publish module to export PulseAudio information through X11 protocol for clients to make use. Don't enable this flag if you want to use a system wide instance. If unsure, enable this flag. 
media-sound/pulseaudio:asyncns - Use libasyncns for asynchronous name resolution.
media-sound/pulseaudio:doc - Build the doxygen-described API documentation.
media-sound/pulseaudio:glib - Enable glib eventloop support
media-sound/pulseaudio:gnome -  Use GConf to store user preferences on streams and so on. Don't enable this flag if you want to use a system wide instance. If unsure, enable this flag. 
media-sound/pulseaudio:oss -  Enable OSS sink/source (output/input). Deprecated, upstream does not support this on systems where other sink/source systems are available (i.e.: Linux). The padsp wrapper is now always build if the system supports OSS at all. 
media-sound/pulseaudio:realtime -  Makes PulseAudio use RealtimeKit (sys-auth/rtkit) to get real-time priority while running. 
media-sound/pulseaudio:system-wide -  Allow preparation and installation of the system-wide init script for PulseAudio. Since this support is only supported for embedded situations, do not enable without reading the upstream instructions at http://pulseaudio.org/wiki/WhatIsWrongWithSystemMode . 
media-sound/qmmp:bs2b - Enable Bauer stereophonic-to-binaural headphone filter
media-sound/qmmp:cover - Enable album cover support
media-sound/qmmp:enca - Detects the character encoding automatically
media-sound/qmmp:kde - Use kde4 notifier system
media-sound/qmmp:lyrics - Fetch track lyrics from the web
media-sound/qmmp:mms - Enable mms support
media-sound/qmmp:mpris - Enable MPRIS support
media-sound/qmmp:notifier - Enable qmmps' notifier system
media-sound/qmmp:projectm - Enable projectm music visualization plugin
media-sound/qmmp:scrobbler - Enable audioscrobbler/last.fm support
media-sound/qmmp:tray - Build tray icon
media-sound/qmmp:udisks - Use udisks plugins to detect removal devices
media-sound/qsampler:libgig - Enable libgig support for loading Gigasampler files and DLS (Downloadable Sounds) Level 1/2 files
media-sound/qtractor:dssi - Enable support for DSSI Soft Synth Interface
media-sound/qtractor:rubberband - Enable support for in-place audio clip pitch-shifting through the rubberband library
media-sound/qtscrobbler:cli - Build commandline client
media-sound/rezound:16bittmp - Use 16bit temporary files (default 32bit float), useful for slower computers
media-sound/rezound:soundtouch - compile with support for soundtouch
media-sound/rhythmbox:daap - Enable support for local network music sharing via daap
media-sound/rhythmbox:upnp - Enable support for local network music sharing via upnp
media-sound/rhythmbox:webkit - Enable context panel plugin.
media-sound/rubyripper:cdrdao - Add support for advanced toc scanning using app-cdr/cdrdao
media-sound/rubyripper:cli - Build command line interface rubyripper
media-sound/rubyripper:normalize - Add support for normalizing audio file volume levels
media-sound/rubyripper:wav - Add support for wavegain
media-sound/shntool:alac - Add support for Apple Lossless Audio Codec files
media-sound/shntool:mac - Add support for Monkey's Audio files
media-sound/sonata:lyrics - Support for lyrics fetching
media-sound/sonata:trayicon - Enable support for trayicon
media-sound/sonic-visualiser:id3tag - Enables ID3 tagging with id3tag library
media-sound/sox:amr - Enables Adaptive Multi-Rate Audio support
media-sound/sox:id3tag - Enables ID3 tagging with id3tag library
media-sound/squeezeboxserver:aac - Enable playback support for AAC (.m4a) encoded files
media-sound/squeezeboxserver:alac - Enable support for alac
media-sound/traverso:lv2 - Add support for Ladspa V2
media-sound/vorbis-tools:kate - Adds support for Ogg Kate subtitles via libkate.
media-sound/vorbis-tools:ogg123 - Build ogg123 player, needs libao and curl
media-sound/xmms2:airplay - Support for airplay format
media-sound/xmms2:asf - Support for Monkey's Audio (APE) format with help of bundled libasf
media-sound/xmms2:gvfs - Transport for glibs virtual filesystem
media-sound/xmms2:ices - Icecast source output plugin
media-sound/xmms2:mac - Support for Monkey's Audio (APE) format with help of media-sound/mac
media-sound/xmms2:mlib-update - Enable building of xmms2-mlib-updater client
media-sound/xmms2:mms - Support for Microsoft Media Server (MMS) streams via libmms
media-sound/xmms2:ofa - Support for Open Fingerprint Architecture (OFA)
media-sound/xmms2:phonehome - This client sends anonymous usage-statistics to the xmms2
media-sound/xmms2:server - Build xmms2 player daemon (otherwise only clients are built)
media-sound/xmms2:sid - Support for C64 SID
media-sound/xmms2:vocoder - Phase vocoder effect plugin
media-sound/xmms2:xml - Enable support for various XML based playlists and sources: RSS, XSPF
media-sound/xmp:audacious - Enable audacious support
media-sound/xwax:alsa - Adds support for ALSA audio input/output.
media-sound/xwax:xwax_decoders_aac - Sets runtime dependencies to support decoding AAC audio.
media-sound/xwax:xwax_decoders_cd - Sets runtime dependencies to support decoding audio from a compact disc.
media-sound/xwax:xwax_decoders_flac - Sets runtime dependencies to support decoding FLAC audio.
media-sound/xwax:xwax_decoders_misc - Sets runtime dependencies to support decoding "other" audio files.
media-sound/xwax:xwax_decoders_mp3 - Sets runtime dependencies to support decoding MP3 audio.
media-sound/xwax:xwax_decoders_ogg - Sets runtime dependencies to support decoding Ogg Vorbis audio.
media-tv/freevo:ivtv - Enables ivtv support
media-tv/freevo:mixer - Enable support for adjusting volume via media-sound/aumix
media-tv/freevo:tv - Enable support for the tv guide plugin
media-tv/freevo:tvtime - Enables tvtime support, additional to tv use flag
media-tv/gentoo-vdr-scripts:nvram - Add support for using nvram-wakeup to set wakeup time in bios
media-tv/mythtv:alsa - Allows MythTV to directly output sound to ALSA devices, this is needed if you are using ALSA dmix or SPDIF. Note, you will have to physically type your device into the MythTV configuration since it will only give you /dev/dsp devices in the drop down.
media-tv/mythtv:altivec - Builds ffmpeg's codec libraries with altivec support.
media-tv/mythtv:autostart - Uses a custom autostart configuration gleaned from experience with MythTV since its early versions and discussed with other MythTV maintainers and users. Does not rely on KDE being installed like most methods do.
media-tv/mythtv:debug - Instructs Qt to use the 'debug' target instead of 'release' target. If your MythTV is crashing or you need a backtrace, you need to compile it with this option otherwise the debugging data is useless.
media-tv/mythtv:directv - Installs the DirecTV channel changing script so that you can configure MythTV to use it to change the channels on your DirecTV box.
media-tv/mythtv:dvb - Enables support for Linux DVB cards. These include all cards that work with digital signals such as ATSC, DVB-T, DVB-C, and DVB-S, QAM-64, and QAM-256.
media-tv/mythtv:faad - Uses external faad library for AAC decoding instead of internal libavcodec for decoding AAC. The faad library supports additional AAC types like AAC-LATM that libavcodec does not support
media-tv/mythtv:ieee1394 - Allows MythTV to communicate and use Firewire enabled Cable boxes. These are typically found in the United States, where such support is required by law. This will also install Firewire test programs and external channel changers if the internal changer does not work.
media-tv/mythtv:jack - Allows MythTV to use JACK as your sound output device. You will have to manually configure the path to your JACK settings.
media-tv/mythtv:lcd - Tells MythTV that you have an instance of app-misc/lcdproc configured on your machine and it should output information such as current time, show name, episode name, etc to that LCD.
media-tv/mythtv:lirc - Adds LIRC support directly to MythTV allowing for built in control via a LIRC device.
media-tv/mythtv:mmx - Builds ffmpeg's codec libraries with mmx support.
media-tv/mythtv:perl - Builds the perl bindings for MythTV. Allows you to write scripts in Perl to control your MythTV setup or communicate with it.
media-tv/mythtv:tiff - Add support for tiff loading and rendering which is only used by media-plugins/mythgallery
media-tv/mythtv:vdpau - enable support of NVIDIA's VDPAU for video playback
media-tv/mythtv:video_cards_nvidia - When combined with the xvmc USE flag, enables NVIDIA specific XvMC extension usage.
media-tv/mythtv:xvmc - Instructs MythTV to use XvMC for its video output. By default, this will use the generic XvMC wrapper unless a specific video card driver is enabled via their VIDEO_CARDS USE flags.
media-tv/tvbrowser:themes - Install extra theme packs
media-tv/xawtv:xext - Enable use of XFree extensions (DGA,VidMode,DPMS)
media-tv/xawtv:zvbi - Enable VBI Decoding Library for Zapping
media-tv/xbmc:midi - Support MIDI files
media-tv/xbmc:rtmp - Enable Real Time Messaging Protocol using librtmp
media-tv/xbmc:vaapi - Enables VAAPI (Video Acceleration API) for hardware decoding
media-tv/xbmc:vdpau - enable support for Video Decode and Presentation API for Unix
media-tv/xbmc:webserver - Enable internal webserver
media-tv/xbmc:xrandr - Support X randr extension
media-tv/xdtv:aqua_theme - Enable graphic theme Aqua-style
media-tv/xdtv:carbone_theme - Adds the Carbone pixmaps theme for the GUI
media-tv/xdtv:schedule - Adds the possibility to schedule tv recording via xdtv_record.sh
media-tv/xdtv:zvbi - Enable VBI Decoding Library for Zapping
media-tv/xmltv:ar - Argentina tv listing grabber
media-tv/xmltv:be - Belgium and Luxemburg tv listing grabber
media-tv/xmltv:brnet - Brazil cable tv listing grabber
media-tv/xmltv:ch - Switzerland bluewin tv listing grabber
media-tv/xmltv:dk - Denmark tv listing grabber
media-tv/xmltv:dtvla - Latin America digital tv listing grabber
media-tv/xmltv:ee - Estonia tv listing grabber
media-tv/xmltv:es - Spain tv listing grabber
media-tv/xmltv:es_laguiatv - Spain alternative grabber
media-tv/xmltv:es_miguiatv - Spain alternative grabber
media-tv/xmltv:eu_epg - EPG grabber for some European countries.
media-tv/xmltv:fi - Finland tv listing grabber
media-tv/xmltv:fr - France tv listing grabber
media-tv/xmltv:hr - Croatia tv listing grabber
media-tv/xmltv:huro - Hungarian tv listing grabber
media-tv/xmltv:is - Iceland tv listing grabber
media-tv/xmltv:it - Italy tv listing grabber
media-tv/xmltv:jp - Japan tv listing grabber
media-tv/xmltv:na_dd - North America tv listing grabber
media-tv/xmltv:na_dtv - North America Direct TV grabber
media-tv/xmltv:na_icons - option for na_dd to download icons
media-tv/xmltv:nc - Caledonie Island tv listing grabber
media-tv/xmltv:nl - Netherlands tv listing grabber
media-tv/xmltv:nl_wolf - Netherlands alternative tv listing grabber
media-tv/xmltv:no - Norway tv listing grabber
media-tv/xmltv:no_gf - Norway Gfeed tv listing grabber
media-tv/xmltv:pt - Portugal tv listing grabber
media-tv/xmltv:re - Reunion Island (France) tv listing grabber
media-tv/xmltv:se_swedb - Sweden tv listing grabber
media-tv/xmltv:tv_check - enable GUI checking
media-tv/xmltv:tv_combiner - enable grabbers combiner
media-tv/xmltv:tv_pick_cgi - enable CGI support
media-tv/xmltv:uk_bleb - Britain tv listing grabber
media-tv/xmltv:uk_rt - Britain alternative tv listing grabber
media-tv/xmltv:za - South Africa tv listing grabber
media-video/arista:faac - Use external faac library for AAC encoding
media-video/arista:nautilus - Add an entry in the Nautilus context menu to transcode media files for a specified device.
media-video/avidemux:aften - Enable A/52 (AC-3) audio encoder support
media-video/avidemux:amr - Enable Adaptive Multi-Rate format support through media-libs/opencore-amr
media-video/chaplin:transcode - Enable DVD ripping and transcoding
media-video/clive:clipboard - Support reading from X clipboard
media-video/clive:pager - Support pager!?
media-video/clive:password - Support password controlled sites
media-video/devede:psyco - psyco python accelerator
media-video/dv2sub:kino - install kino plugin
media-video/dvd-slideshow:themes - Install theme pack
media-video/dvdrip:fping - Enables fping support for cluster rendering
media-video/dvdrip:subtitles - Enables support for subtitle ripping
media-video/ffmpeg:3dnowext -  Enable manually-optimised routines using the AMD 3DNow!Ex SIMD instruction set, present in modern AMD CPUs. (Check for 3dnowext in /proc/cpuinfo to know whether your CPU supports it). 
media-video/ffmpeg:amr - Enables Adaptive Multi-Rate Audio support
media-video/ffmpeg:cpudetection - Enables runtime CPU detection (useful for bindist, compatibility on other CPUs)
media-video/ffmpeg:dirac - Enable Dirac video support (an advanced royalty-free video compression format) via the reference library: dirac.
media-video/ffmpeg:faac - Use external faac library for AAC encoding
media-video/ffmpeg:faad - Use external faad library for AAC decoding (instead of internal libavcodec support)
media-video/ffmpeg:frei0r - Enable frei0r wrapping in libavfilter
media-video/ffmpeg:hardcoded-tables - Use pre-calculated tables rather than calculating them on the fly.
media-video/ffmpeg:mmxext - Enables mmx2 support
media-video/ffmpeg:network - Enables network streaming support
media-video/ffmpeg:pic - Force shared libraries to be built as PIC (this is slower)
media-video/ffmpeg:qt-faststart - Build and install qt-faststart application
media-video/ffmpeg:rtmp - Enable Real Time Messaging Protocol using librtmp
media-video/ffmpeg:schroedinger - Enable Dirac video support (an advanced royalty-free video compression format) via libschroedinger (high-speed implementation in C of the Dirac codec).
media-video/ffmpeg:ssse3 - faster floating point optimization for SSSE3 capable chips (Intel Core 2 and later chips)
media-video/ffmpeg:vaapi - Enables VAAPI (Video Acceleration API) for hardware decoding
media-video/ffmpeg:vdpau - Enables VDPAU decoders (requires nVidia video cards to offload CPU processing to video card
media-video/ffmpeg:vpx - Enables vp8 codec support using libvpx: Decoding vp8 does not require this to be enabled but libvpx can also be used for decoding; encoding vp8 requires this useflag to be enabled though.
media-video/ffmpeg2theora:kate - Adds support for Ogg Kate subtitles via libkate.
media-video/google2srt:html - Install HTML documentation
media-video/griffith:csv - Enable proper support for csv import (respectively auto-detection encoding of csv files)
media-video/h264enc:ogm - Support for OGM container format
media-video/hwdecode-demos:vaapi - Enables VAAPI (Video Acceleration API) for hardware decoding
media-video/hwdecode-demos:vdpau - Enables VDPAU decoders (requires nVidia video cards to offload CPU processing to video card
media-video/kino:gpac - Enable GPAC support when exporting to 3GPP format
media-video/kmplayer:npp - Compile the npp backend that plays xembed style browser plugins.
media-video/lives:libvisual - Enable libvisual support
media-video/mediainfo:libmms - Support for Microsoft Media Server (MMS) streams via libmms
media-video/mjpegtools:yv12 - Enables support for the YV12 pixel format
media-video/motiontrack:multiprocess - Enables multi-process support (SMP/cluster) for motiontrack programs
media-video/mplayer:3dnowext - Enable 3dnowext cpu instructions
media-video/mplayer:amr - Enables Adaptive Multi-Rate format support
media-video/mplayer:ass - SRT/SSA/ASS (SubRip / SubStation Alpha) subtitle support
media-video/mplayer:bl - Blinkenlights video output
media-video/mplayer:bluray - Enable playback of Blu-ray filesystems
media-video/mplayer:bs2b - Enable Bauer stereophonic-to-binaural headphone filter
media-video/mplayer:cdio - Use libcdio for CD support (instead of cdparanoia)
media-video/mplayer:cpudetection - Enables runtime CPU detection (useful for bindist, compatibility on other CPUs)
media-video/mplayer:custom-cpuopts - Fine-tune custom CPU optimizations (UNSUPPORTED)
media-video/mplayer:dirac - Enable Dirac video support (an advanced royalty-free video compression format) via the reference library: dirac.
media-video/mplayer:dvdnav - Use forked libdvdnav, navigate menus in GUIs
media-video/mplayer:dxr3 - Enable DXR3/H+ video output
media-video/mplayer:enca - Enables support for charset discovery and conversion
media-video/mplayer:external-ffmpeg - Use shared FFmpeg libraries instead of static bundled ones. Discouraged by upstream.
media-video/mplayer:faac - Use external faac library for AAC encoding
media-video/mplayer:faad - Use external faad library for AAC decoding
media-video/mplayer:gmplayer - Build gmplayer, a GTK+ MPlayer gui (UNSUPPORTED)
media-video/mplayer:libmpeg2 - Build support for mpeg2 over media-libs/libmpeg2 rather than using ffmpeg.
media-video/mplayer:live - Enables live.com streaming media support
media-video/mplayer:md5sum - Enables md5sum video output
media-video/mplayer:mmxext - Enables mmx2 support
media-video/mplayer:mng - MNG input support
media-video/mplayer:mpg123 - Enable support for mp3 decoding over media-sound/mpg123.
media-video/mplayer:network - Enables network streaming support
media-video/mplayer:nut - Enables support for the NUT container format
media-video/mplayer:osdmenu - Enables support for on-screen display (OSD) menus
media-video/mplayer:pnm - Add PNM video output option, to create PPM/PGM/PGMYUV images
media-video/mplayer:pvr - Enable Video4Linux2 MPEG PVR
media-video/mplayer:radio - Enable V4L2 radio interface and support
media-video/mplayer:rar - Enable Unique RAR File Library
media-video/mplayer:real - Adds real audo/video support
media-video/mplayer:rtc - Enables usage of the linux real time clock. The alternative is software emulation of rtc
media-video/mplayer:rtmp - Enables RTMPDump Streaming Media support
media-video/mplayer:schroedinger - Enable Dirac video support (an advanced royalty-free video compression format) via libschroedinger (high-speed implementation in C of the Dirac codec).
media-video/mplayer:shm - Enable support for shm
media-video/mplayer:ssse3 - faster floating point optimization for SSSE3 capable chips (Intel Core 2 and later chips)
media-video/mplayer:teletext - Support for TV teletext interface
media-video/mplayer:tga - Enables Targa video output
media-video/mplayer:toolame - Enable toolame MPEG-2 encoding
media-video/mplayer:tremor - Enable internal support for Vorbis
media-video/mplayer:twolame - Enable twolame MPEG-2 encoding
media-video/mplayer:vdpau - Enables experimental VDPAU support (requires nVidia video cards) to offload MPEG2/MPEG4/VC1/WMV CPU processing to video card
media-video/mplayer:vidix - Support for vidix video output
media-video/mplayer:vpx - Enables vp8 codec support using libvpx: Decoding vp8 does not require this to be enabled but libvpx can also be used for decoding; encoding vp8 requires this useflag to be enabled though.
media-video/mplayer:xanim - Enables support for xanim based codecs
media-video/mplayer:xvmc - Enables X-Video Motion Compensation support
media-video/mplayer:zoran - Enables ZR360[56]7/ZR36060 video output
media-video/ogmrip:ogm - Support for OGM container format
media-video/ogmrip:srt - Support for SRT subtitle format
media-video/rtmpdump:gnutls - Use GnuTLS library instead of the default OpenSSL
media-video/rtmpdump:polarssl - Use PolarSSL library instead of the default OpenSSL
media-video/totem:bluetooth - Enable support for user-presence detection via the user's bluetooth handset using net-wireless/bluez
media-video/totem:galago - Allow Totem to set your IM client to "away" when a movie is playing in fullscreen using dev-libs/libgalago
media-video/totem:iplayer - Enable BBC player support
media-video/totem:lirc - Enable support for controlling Totem with a remote control using app-misc/lirc
media-video/totem:nautilus - Enable the nautilus extension
media-video/totem:python - Build support for dev-lang/python plugins
media-video/totem:tracker - Enable support for searching media files using the indexer app-misc/tracker
media-video/totem:upnp - Enable DLNA support through media-video/coherence
media-video/totem:youtube - Enable youtube plugin
media-video/transcode:extrafilters - Install some filters only if we ask for them
media-video/transcode:fame - Enables libfame support
media-video/transcode:mjpeg - Enables mjpegtools support
media-video/transcode:network - Enables network streaming support
media-video/transcode:nuv - NuppelVideo container format demuxing
media-video/transcode:postproc - Build with ffmpeg libpostproc support
media-video/tsmuxer:qt4 - Installs tsMuxerGUI (needs Qt4)
media-video/undvd:ogm - Support for OGM container format
media-video/ushare:dlna - Add DLNA (media-libs/libdlna) support
media-video/vdr:analogtv - Add support for the analogtv plugin
media-video/vdr:atsc - Support for NorthAmerican Broadcast ( rudimentary )
media-video/vdr:cmdreccmdi18n - loads translated commands and reccommands files if existing
media-video/vdr:cmdsubmenu - Allows the creation of submenus in the commands menu
media-video/vdr:cutterlimit - Limit IO bandwith used for cutting
media-video/vdr:cutterqueue - Adds a queue of recordings to be cutted
media-video/vdr:cuttime - Adjust starttime of cutted recording by length of cut out parts
media-video/vdr:ddepgentry - remove duplicate EPG entries
media-video/vdr:deltimeshiftrec - Auto delete timeshift recordings
media-video/vdr:dolbyinrec - add a dedicated switch to control recording of dolby digital
media-video/vdr:dvbplayer - Use some special mpeg-repacker features. Most usable for old recordings or software output devices.
media-video/vdr:dvbsetup - Setup for AC3 transfer, disable primary tuner
media-video/vdr:dvdarchive - DMH DVD - Archiv ( used by vdr-burn-0.1.0_* )
media-video/vdr:dvdchapjump - Jump on capitels on DMH DVD - Archiv
media-video/vdr:dvlfriendlyfnames - filter file names on recording
media-video/vdr:dvlrecscriptaddon - enhancement for record-script
media-video/vdr:dvlvidprefer - controls video-dir choice on recording
media-video/vdr:dxr3 - Enable tweaks to improve vdr behaviour on dxr3-cards
media-video/vdr:em84xx - Add support for em84xx plugin
media-video/vdr:graphtft - support for grapftft plugin up from vdr-graphtft-0.1.7
media-video/vdr:hardlinkcutter - Speed up cutting by hardlinking unchanged files
media-video/vdr:iptv - Enables channel parameters for vdr-iptv and other input plugins
media-video/vdr:jumpplay - Enables automatic jumping over cut marks while watching a recording
media-video/vdr:liemikuutio - Formerly known as AIO (all-in-one) patch, adds some nice must haves, plus changes from extensions patch
media-video/vdr:lircsettings - Allows to change lirc settings delay, freq and timeout values in OSD
media-video/vdr:livebuffer - does timeshifting/background recording all the time, allows to rewind live TV
media-video/vdr:lnbshare - Enables support for two or more dvb cards sharing the same cable to the lnb
media-video/vdr:mainmenuhooks - Allows to replace main menu entries by some special plugins (like epgsearch, extrecmenu, ...)
media-video/vdr:menuorg - Enables support for the menuorg-plugin
media-video/vdr:noepg - Adds code to selectively disable epg-reception for specific channels
media-video/vdr:osdmaxitems - Support for text2skin
media-video/vdr:parentalrating - Support Parental Rating
media-video/vdr:pinplugin - Support for pin plugin
media-video/vdr:rotor - Enable support for plugin vdr-rotor for dish-positioner.
media-video/vdr:settime - set system time per script instead of via syscal
media-video/vdr:setup - Enable support for the plugin vdr-setup
media-video/vdr:softosd - Soft OSD fading with FF-Cards
media-video/vdr:sortrecords - allows to change sort order of recordings
media-video/vdr:sourcecaps - Adds the ability to define capabilities of dvb-cards (e.g. card1 can receive Sat @28.2E)
media-video/vdr:syncearly - start live display as soon as possible, not waiting for sync of audio and video
media-video/vdr:timercmd - Adds submenu for user defined commands in timer menu
media-video/vdr:timerinfo - Show with chars +/- if space on HD will suffice for a timer
media-video/vdr:ttxtsubs - support for ttxtsubs plugin
media-video/vdr:validinput - Signal if it is possible to go left/right in lists with chars < >
media-video/vdr:volctrl - allows volume control using left/right keys
media-video/vdr:wareagleicon - Replace original icon set in menu
media-video/vdr:yaepg - Enables support for the plugin vdr-yaepg
media-video/vlc:X - Enables support for, e.g., fullscreen mode via the X Window System. By itself, this flag does not build a graphical interface.
media-video/vlc:atmo - Enables support for AtmoLight (homebrew Ambient Lighting Technology)
media-video/vlc:dc1394 - Enables IIDC cameras support.
media-video/vlc:dirac - Enable Dirac video support (an advanced royalty-free video compression format) via the reference library: dirac.
media-video/vlc:fluidsynth - Enables Fluidsynth MIDI software synthesis (with external sound fonts).
media-video/vlc:gcrypt - Enables cryptography support via libgcrypt.
media-video/vlc:gme - Enables support for media-libs/game-music-emu for playing various video game music formats.
media-video/vlc:gnome - Adds support for GNOME's filesystem abstraction layer, gnome-base/gnome-vfs. This flag is not GUI-related.
media-video/vlc:httpd - Enables a web based interface for vlc.
media-video/vlc:id3tag - Enables id3tag metadata reader plugin.
media-video/vlc:kate - Adds support for Ogg Kate subtitles via libkate.
media-video/vlc:libass - Enables subtitles support using libass.
media-video/vlc:libproxy - Enables support for proxy settings in the HTTP access module.
media-video/vlc:libtiger - Enables Ogg Kate subtitles rendering using libtiger.
media-video/vlc:libv4l - Enables Libv4l Video4Linux support.
media-video/vlc:libv4l2 - Enables Libv4l2 Video4Linux2 support (for conversion from various video formats to standard ones, needed to use v4l2 devices with strange formats).
media-video/vlc:live - Enables live555 streaming media support (client support for rtsp).
media-video/vlc:matroska - Enables matroska support using reference libraries (fallback on other existing matroska support if disabled, i.e., matroska enabled FFmpeg)
media-video/vlc:optimisememory - Enable optimisation for memory rather than performance.
media-video/vlc:projectm - Enables the projectM visualization plugin.
media-video/vlc:pvr - Enables PVR cards access module.
media-video/vlc:qt4 - Builds a x11-libs/qt based frontend. It is now the most up-to-date graphical interface available.
media-video/vlc:remoteosd - Enables RemoteOSD plugin (VNC client as video filter).
media-video/vlc:rtsp - Enables real audio and RTSP modules.
media-video/vlc:run-as-root - Allows vlc to start for root. Don't enable this unless you have a very specific (e.g. embedded) need for it!
media-video/vlc:schroedinger - Enable Dirac video support (an advanced royalty-free video compression format) via libschroedinger (high-speed implementation in C of the Dirac codec).
media-video/vlc:sdl-image - Enables sdl image video decoder (depends on sdl)
media-video/vlc:shine - Enables shine fixed point mp3 encoder.
media-video/vlc:shout - Enables libshout output.
media-video/vlc:skins - Enables support for the skins2 interface.
media-video/vlc:stream - Enables sout module for audio/video data streaming/transcoding/etc..
media-video/vlc:twolame - Enables twolame support (MPEG Audio Layer 2 encoder).
media-video/vlc:upnp - Enables support for Intel UPnP stack.
media-video/vlc:vaapi - Enables VAAPI (Video Acceleration API) for hardware decoding
media-video/vlc:vcdx - Enables VCD with navigation via libvcdinfo (depends on cdio)
media-video/vlc:vlm - New videolan (media) manager (vlm), a little manager designed to launch and manage multiple streams from within one instance of VLC.
media-video/vlc:wma-fixed - Enables fixed point WMA decoder.
media-video/vlc:zvbi - Enables support for teletext subtitles via the zvbi library.
media-video/winki:mjpeg - Enables mjpegtools support
media-video/xine-ui:vdr - Enables Video Disk Recorder support
net-analyzer/aimsniff:http - Install the WAS (Web AIM Sniff) frontend
net-analyzer/barnyard:sguil - Enable sguil (The Analyst Console for Network Security Monitoring) support
net-analyzer/barnyard2:aruba - Enable Aruba support
net-analyzer/barnyard2:gre - Enable GRE support
net-analyzer/barnyard2:mpls - Enable support for mpls networks
net-analyzer/base:signatures - Install community signatures from net-analyzer/snort
net-analyzer/bmon:rrdtool - Enables net-analyzer/rrdtool support
net-analyzer/bwm-ng:csv - Enable csv output
net-analyzer/bwm-ng:html - Enable html output
net-analyzer/cacti:doc - install html documentation
net-analyzer/echoping:http - enable support for http protocol.
net-analyzer/echoping:icp - enable support for ICP (used to monitor proxies).
net-analyzer/echoping:priority - enable socket priority support.
net-analyzer/echoping:smtp - enable support for SMTP protocol.
net-analyzer/echoping:tos - enable support for TOS (TYpe Of Service).
net-analyzer/fprobe:messages - enable console messages
net-analyzer/lilac:nmap - Installs nmap which can be used to automatically discover devices to monitor.
net-analyzer/munin:irc - installs deps for monitoring IRC
net-analyzer/nagios-core:lighttpd - install www-servers/lighttpd config
net-analyzer/nagios-core:web - enable web interface
net-analyzer/nagios-nrpe:command-args - allow clients to specify command arguments
net-analyzer/nagios-plugins:nagios-dns - installs deps for dns monitoring
net-analyzer/nagios-plugins:nagios-game - installs deps for monitoring games-util/qstat
net-analyzer/nagios-plugins:nagios-ntp - installs deps for ntp monitoring
net-analyzer/nagios-plugins:nagios-ping - installs deps for fancy ping monitoring
net-analyzer/nagios-plugins:nagios-ssh - installs deps for monitoring ssh
net-analyzer/nagios-plugins:ups - installs deps for monitoring Network-UPS (sys-power/nut)
net-analyzer/nagvis:automap - Enable automated map generation using media-gfx/graphviz
net-analyzer/net-snmp:diskio - Enable the use of diskio mibs
net-analyzer/net-snmp:elf - Enable the use of elf utils to check uptime on some systems
net-analyzer/net-snmp:extensible - build deprecated extensible mib module (extend is successor)
net-analyzer/net-snmp:mfd-rewrites - Use MFD rewrites of mib modules where available
net-analyzer/net-snmp:rpm - Enable the rpm snmp probing
net-analyzer/net-snmp:sendmail - Enable sendmail statistics monitoring
net-analyzer/net-snmp:smux - Enable the smux MIBS module
net-analyzer/nfdump:compat15 - Enable read support for nfdump data files created with nfdump 1.5.x
net-analyzer/nfdump:ftconv - Build the flow-tools to nfdump converter
net-analyzer/nfdump:nfprofile - Build nfprofile used by NfSen
net-analyzer/nfdump:sflow - Build sflow collector sfcpad
net-analyzer/pchar:pcap - Use the net-libs/libpcap library
net-analyzer/pmacct:64bit - Use 64bit counters instead of 32bit ones
net-analyzer/pmacct:ulog - Enable ULOG support
net-analyzer/rrdcollect:exec - Enable exec:/// support
net-analyzer/rrdcollect:pcap - Use net-libs/libpcap for packet capturing
net-analyzer/rrdtool:nls - Enable native language support (using intltool)
net-analyzer/rrdtool:rrdcgi - Build rrdcgi support
net-analyzer/sancp:sguil - Enable sguil (The Analyst Console for Network Security Monitoring) support
net-analyzer/scanlogd:nids - Use net-libs/libnids for packet capturing
net-analyzer/scanlogd:pcap - Use net-libs/libpcap for packet capturing
net-analyzer/scapy:pyx - Enable dev-python/pyx support for psdump/pdfdump commands
net-analyzer/scapy:tcpreplay - Enable net-analyzer/tcpreply support for fast packet replay
net-analyzer/scapy:visual - Enable dev-python/visual support for 3d graphs
net-analyzer/smokeping:speedy - Use dev-perl/SpeedyCGI instead of perl to speed up cgi scripts
net-analyzer/snort:active-response -  Enables support for automatically sending TCP resets and ICMP unreachable messages to terminate connections. Used with inline deployments. 
net-analyzer/snort:aruba -  Adds support for monitoring wireless traffic using a Aruba Mobility Controler. 
net-analyzer/snort:decoder-preprocessor-rules -  Added support to provide action control (alert, drop, pass, etc) over preprocessor and decoder generated events. 
net-analyzer/snort:dynamicplugin -  Enable ability to dynamically load preprocessors, detection engine, and rules library. This is required if you want to use shared object (SO) snort rules. 
net-analyzer/snort:flexresp -  (DEPRECIATED) Original method for enabling connection tearing for inline deployments. Replaced with flexresp3 in Snort-2.9.0. 
net-analyzer/snort:flexresp2 -  (DEPRECIATED) Replaced flexresp for enabling connection tearing for inline deployments. Replaced with flexresp3 in Snort-2.9.0. 
net-analyzer/snort:flexresp3 -  Enables support for new flexable response preprocessor for enabling connection tearing for inline deployments. Replaces flexresp and flexresp2. 
net-analyzer/snort:gre -  Enable support for inspecting and processing Generic Routing Encapsulation (GRE) packet headders. Only needed if you are monitoring GRE tunnels. 
net-analyzer/snort:inline -  (DEPRECIATED) Enables support for deploying snort inline. Uses net-firewall/iptables, via libipq, rather than net-libs/libpcap. Replaced by DAQ in Snort-2.9.0 
net-analyzer/snort:inline-init-failopen -  Enables support to allow traffic to pass (fail-open) through inline deployments while snort is starting and not ready to begin inspecting traffic. If this option is not enabled, network traffic will not pass (fail-closed) until snort has fully started and is ready to perform packet inspection. 
net-analyzer/snort:linux-smp-stats -  Enable accurate statistics reporting through /proc on systems with multipule processors. 
net-analyzer/snort:mpls -  Enables support for processing and inspecting Multiprotocol Label Switching MPLS network network traffic. Only needed if you are monitoring an MPLS network. 
net-analyzer/snort:normalizer -  Enables support for normalizing packets in inline deployments to help minimize the chances of detection evasion. 
net-analyzer/snort:perfprofiling -  Enables support for preprocessor and rule performance profiling using the perfmonitor preprocessor. 
net-analyzer/snort:ppm -  Enables support for setting per rule or per packet latency limits. Helps protect against introducing network latency with inline deployments. 
net-analyzer/snort:react -  Enables support for the react rule keyword. Supports interception, termination, and redirection of HTTP connections. 
net-analyzer/snort:reload -  Enables support for reloading a configuration without restarting snort. 
net-analyzer/snort:reload-error-restart -  Enables support for completely restarting snort if an error is detected durring a reload. 
net-analyzer/snort:targetbased -  Enables support in snort for using a host attibute XML file (attribute_table.dtd). This file needs to be created by the user and should define the IP address, operating system, and services for all hosts on the monitored network. This is cumbersome, but can improve intrusion detection accuracy. 
net-analyzer/snort:timestats -  (DEPRECIATED) Enables support for printing packet stats on a per hour and per protocol breakdown. Depreciated in Snort-2.9.0. 
net-analyzer/snort:zlib -  Enables HTTP inspection of compressed web traffic. Requires dynamicplugin be enabled. 
net-analyzer/symon:perl - Enables a generic perl symux client
net-analyzer/symon:symon - Enables the system monitor. Offers no functionality but monitoring and forwarding of measured data
net-analyzer/symon:symux - Enables the multiplexer which stores incoming symon streams on disk in RRD (net-analyzer/rrdtool) files
net-analyzer/tcpdump:chroot - Enable chrooting when dropping privileges
net-analyzer/tcpdump:smi - Build with net-libs/libsmi to load MIBs on the fly to decode SNMP packets
net-analyzer/tcpreplay:pcapnav - Enable if you want the jump to byte offset feature via net-libs/libpcapnav
net-analyzer/tcpreplay:tcpdump - Use net-analyzer/tcpdump for packet decoding feature 
net-analyzer/wireshark:ares - Use GNU net-dns/c-ares library to resolve DNS names
net-analyzer/wireshark:doc-pdf - Build documentation in pdf format (US and a4 paper sizes)
net-analyzer/wireshark:gcrypt - Use GNU crypto library (dev-libs/libgcrypt) to decrypt ipsec traffic
net-analyzer/wireshark:pcap - Use net-libs/libpcap for network packet capturing (build dumpcap, rawshark)
net-analyzer/wireshark:smi - Use net-libs/libsmi to resolve numeric OIDs into human readable format
net-analyzer/zabbix:agent - Enable zabbix agent (for to-be-monitored machines)
net-analyzer/zabbix:frontend - Enable zabbix web frontend
net-analyzer/zabbix:openipmi - Enable openipmi things
net-analyzer/zabbix:proxy - Enable proxy support
net-analyzer/zabbix:server - Enable zabbix server
net-analyzer/zabbix:ssh - Enable ssh.run items
net-dialup/capi4k-utils:fax - Install capi-fax demo programs
net-dialup/capi4k-utils:pppd - Installs pppdcapiplugin modules
net-dialup/capi4k-utils:rcapid - Installs rcapid daemon
net-dialup/freeradius:edirectory - Enables Novell eDirectory integration
net-dialup/freeradius:frascend - Enables Ascend binary mode
net-dialup/freeradius:frxp - Enables experimental modules
net-dialup/freeradius:udpfromto - Compile in UDPFROMTO support (enables freeradius to specify source address correctly in multi-homed setups)
net-dialup/freeradius-client:scp - Add service type hints derived from username prefix
net-dialup/freeradius-client:shadow - Enable shadow password support
net-dialup/mgetty:fax - Enables fax support
net-dialup/mgetty:fidonet - Enables FidoNet support
net-dialup/misdn:ecaggressive - Make the selected echo canceller a little more aggressive
net-dialup/misdn:eckb1 - Use the KB1 echo canceller
net-dialup/misdn:ecmark2 - Use the MARK2 echo canceller
net-dialup/misdn:ecmg2 - Use the MG2 echo canceller (default)
net-dialup/ppp:activefilter - Enables active filter support
net-dialup/ppp:atm - Enables ATM (Asynchronous Transfer Mode) protocol support
net-dialup/ppp:dhcp - Installs PPP DHCP client plugin for IP address allocation by a DHCP server (see http://www.netservers.co.uk/gpl/)
net-dialup/ppp:eap-tls - Enables support for Extensible Authentication Protocol and Transport Level Security (see http://eaptls.spe.net/index.html)
net-dialup/ppp:gtk - Installs GTK+ password prompting program that can be used by passprompt.so PPP plugin for reading the password from a X11 input terminal
net-dialup/ppp:ipv6 - Enables support for IP version 6
net-dialup/ppp:mppe-mppc - Enables support for MPPC (Microsoft Point-to-Point Compression) - NEEDS A PATCHED KERNEL <=2.6.14 (see http://mppe-mppc.alphacron.de)
net-dialup/ppp:pam - Enables PAM (Pluggable Authentication Modules) support
net-dialup/ppp:radius - Enables RADIUS support
net-dialup/pptpd:gre-extreme-debug - Log all GRE accepted packages when in debug mode (required if you want upstream support)
net-dialup/xl2tpd:dnsretry - Patch for host lookup retries, activated by redial feature
net-dns/avahi:autoipd - Build and install the IPv4LL (RFC3927) network address configuration daemon
net-dns/avahi:bookmarks - Install the avahi-bookmarks application (requires dev-python/twisted)
net-dns/avahi:howl-compat - Enable compat libraries for howl
net-dns/avahi:mdnsresponder-compat - Enable compat libraries for mDNSResponder
net-dns/bind:dlz - Enables dynamic loaded zones, 3rd party extension
net-dns/bind:gssapi - Enable gssapi support
net-dns/bind:resolvconf - Enable support for net-dns/openresolv
net-dns/bind:sdb-ldap - Enables ldap-sdb backend
net-dns/bind:urandom - Use /dev/urandom instead of /dev/random
net-dns/bind-tools:urandom - Use /dev/urandom instead of /dev/random
net-dns/dnsmasq:dhcp - Enable support for reading ISC DHCPd lease files
net-dns/dnsmasq:tftp - Enables built in TFTP server for netbooting
net-dns/maradns:authonly - Allows one to build only authoritative DNS server
net-dns/mydns:alias - Enable David Phillips aliasing
net-dns/mydns:status - Enable the STATUS opcode to check server status
net-dns/pdns:opendbx - Enable the OpenDBX backend
net-dns/pdnsd:isdn - Enable ISDN features
net-dns/pdnsd:nptl -  Linux-only: override auto-detection of the system threading implementation and force usage of the Native Posix Thread Library. 
net-dns/pdnsd:underscores -  Enable support for domain names containing underscores 
net-dns/pdnsd:urandom -  Linux-only: use /dev/urandom (pseudo-random number generation) instead of the default use of random() PRNG. 
net-dns/unbound:gost - Enable GOST support
net-dns/unbound:libevent - Use dev-libs/libevent instead of internal select based events
net-firewall/arno-iptables-firewall:plugins - Install optional plugins
net-firewall/ipsec-tools:hybrid - Makes available both mode-cfg and xauth support
net-firewall/ipsec-tools:idea - Enable support for the patented IDEA algorithm
net-firewall/ipsec-tools:nat - Enable NAT-Traversal
net-firewall/ipsec-tools:rc5 - Enable support for the patented RC5 algorithm
net-firewall/nufw:nfconntrack - Use netfilter_conntrack
net-firewall/nufw:nfqueue - Use NFQUEUE instead of QUEUE
net-firewall/nufw:pam_nuauth - Add support for pam nufw from PAM
net-firewall/nufw:plaintext - Add support for authentication with plaintext files
net-fs/autofs:hesiod - Install hesiod module
net-fs/autofs:ldap - Install LDAP module
net-fs/autofs:sasl - Enable SASL support in the LDAP module
net-fs/coda:client - Build and install the client components of coda filesystem. At least one of client or server should be enabled.
net-fs/coda:coda_layout - Use legacy filesystem layout instead of FHS compliant one. Note: /coda symlink is installed unconditionally when FHS layout is used. Therefore the /coda namespace is preserved with either layout.
net-fs/coda:coda_symlinks - Install legacy symlinks when FHS layout has been selected (-coda_layout). You should only need this if you use local scripts or 3rd party apps relying on precise layout. Note: /coda symlink is installed unconditionally, so the namespace is preserved in any case.
net-fs/coda:server - Build and install the server components of coda filesystem. Note: at least one of client/server flags must be enabled.
net-fs/netatalk:xfs - Enable support for XFS Quota
net-fs/nfs-utils:nfsv3 - Enable support for NFSv3
net-fs/nfs-utils:nfsv4 - Enable support for NFSv4
net-fs/nfs-utils:nonfsv4 - Disable support for NFSv4
net-fs/samba:addns - Enable AD DNS integration
net-fs/samba:ads - Enable Active Directory support
net-fs/samba:aio - Enable asynchronous IO support
net-fs/samba:client - Enables the client part
net-fs/samba:cluster - Enable support for clustering
net-fs/samba:dso - Enable dso support
net-fs/samba:ldb - Enable the ldb tools
net-fs/samba:netapi - Enable building of netapi bits
net-fs/samba:quota - Enables support for user quotas
net-fs/samba:server - Enables the server part
net-fs/samba:smbclient - Enable smbclient tool
net-fs/samba:smbsharemodes - Enable special smb share modes (?) 
net-fs/samba:swat - Enables support for swat configuration gui
net-fs/samba:tools - Enable extra tools
net-fs/samba:winbind - Enables support for the winbind auth daemon
net-fs/smbnetfs:gnome - Use the gnome-base/gnome-keyring for password management.
net-ftp/ftpcube:sftp - Enable sftp connection support
net-ftp/proftpd:authfile - Enable support for the auth-file module
net-ftp/proftpd:ban - Enable support for the mod_ban module
net-ftp/proftpd:case - Enable support for the mod_case module
net-ftp/proftpd:ctrls - Enable support for the mod_ctrls and mod_ctrls_admin modules
net-ftp/proftpd:deflate - Enable support for the mod_deflate module
net-ftp/proftpd:exec - Enable support for the mod_exec module. WARNING: this could be a security risk
net-ftp/proftpd:ident - Enable support for the mod_ident module
net-ftp/proftpd:ifsession - Enable support for the ifsession module
net-ftp/proftpd:ratio - Enable support for the mod_ratio module
net-ftp/proftpd:readme - Enable support for the mod_readme module
net-ftp/proftpd:rewrite - Enable support for the rewrite module
net-ftp/proftpd:sftp - Enable support for the mod_sftp module and optionally mod_sftp_sql and mod_sftp_pam if matching USE flags are enabled
net-ftp/proftpd:shaper - Enable support for the mod_shaper module
net-ftp/proftpd:sitemisc - Enable support for the sitemisc module
net-ftp/proftpd:softquota - Enable support for the quotatab module
net-ftp/proftpd:trace - Build with trace support. Should not be enabled on production servers
net-ftp/proftpd:vroot - Enable support for the virtual root module
net-ftp/pure-ftpd:anondel - Permit anonymous to delete files
net-ftp/pure-ftpd:anonperm - Permit anonymous to change file permissions
net-ftp/pure-ftpd:anonren - Permit anonymous to rename files
net-ftp/pure-ftpd:anonres - Permit anonymous to resume file transfers
net-ftp/pure-ftpd:charconv - Enables charset conversion
net-ftp/pure-ftpd:noiplog - Disables logging of IP addresses
net-ftp/pure-ftpd:paranoidmsg - Display paranoid messages instead of normal ones
net-ftp/pure-ftpd:sysquota - Enables system quota support (needs sys-fs/quota) 
net-ftp/pure-ftpd:vchroot - Enable support for virtual chroot (possible security risk)
net-ftp/twoftpd:breakrfc - Break RFC compliance to allow control symbols in filenames (required for some (e.g. cp1251) encodings, use with caution).
net-im/bitlbee:libevent - Use libevent for event handling
net-im/bitlbee:nss - Use NSS for SSL support in MSN and Jabber
net-im/bitlbee:otr - Enable support for encrypted conversations
net-im/bitlbee:plugins - Enable support for plugins
net-im/bitlbee:purple - Use libpurple instead of the built-in IM protocol support
net-im/bitlbee:twitter - Enable Twitter protocol support
net-im/centerim:gadu - Enable support for the Gadu-Gadu protocol
net-im/centerim:irc - Enable support for the IRC protocol
net-im/centerim:lj - Enable support for the LiveJournal weblog system
net-im/centerim:otr - Enable encrypted conversations
net-im/climm:gloox - Enable support for Jabber/XMPP using gloox
net-im/climm:otr - Enable encrypted conversations
net-im/ejabberd:captcha - Support for CAPTCHA Forms (XEP-158)
net-im/ejabberd:mod_irc - Build irc gateway 
net-im/ejabberd:mod_muc - Build Multi User Chat module
net-im/ejabberd:mod_proxy65 - Support for SOCKS5 Bytestreams (XEP-0065)
net-im/ejabberd:mod_pubsub - Build Pubsub module
net-im/ejabberd:mod_srl - Build LDAP shared roster module (https://alioth.debian.org/projects/ejabberd-msrl/)
net-im/ejabberd:mod_statsdx - Measures several statistics, and provides a new section in ejabberd Web Admin to view them.
net-im/ejabberd:web - Enable web admin interface
net-im/ekg2:extra - Enable following plugins: autoresponder, polchat, rivchat, rot13, xmsg.
net-im/ekg2:gadu - Enable Gadu-Gadu protocol support (requires net-libs/libgadu).
net-im/ekg2:gif - GIF token support for Gadu-Gadu protocol.
net-im/ekg2:gnutls - Enable SSL/TLS support through GnuTLS (for jabber plugin). If 'ssl' is set too, GnuTLS will be used.
net-im/ekg2:gpg - Enable jabber message encryption through app-crypt/gpgme.
net-im/ekg2:inotify - Enable inotify-based filesystem moniotoring support for xmsg&mail plugins.
net-im/ekg2:irc - Enable IRC protocol support.
net-im/ekg2:jogger - Enable support for Jogger.pl jabber bot message parsing plugin.
net-im/ekg2:jpeg - JPEG token support for Gadu-Gadu protocol.
net-im/ekg2:mail - Enable mailbox/maildir monitoring plugin.
net-im/ekg2:minimal - Don't build following plugins: ioctld, logs, rc.
net-im/ekg2:oracle - Support logging messages into Oracle database.
net-im/ekg2:pcap - Enable Gadu-Gadu protocol sniffer plugin (requires net-libs/libpcap).
net-im/ekg2:remote - Enable remote UI plugin allowing to connect to running EKG2 using net-im/ekg2-remote.
net-im/ekg2:sim - Enable 'sim' plugin which provides asymmetric encryption of messages used by few unofficial Gadu-Gadu clients (requires dev-libs/openssl).
net-im/ekg2:sms - Enable SMS sending plugin.
net-im/ekg2:sqlite - Support logging messages into SQLite2 database. If 'sqlite3' is set too, it will be used instead.
net-im/ekg2:sqlite3 - Support logging messages into SQLite3 database. If 'sqlite' is set too, SQLite3 will be used.
net-im/ekg2:srv - Use SRV-capable resolver through libresolv.
net-im/ekg2:ssl - Enable SSL/TLS support through OpenSSL (for jabber plugin). If 'gnutls' is set too, it will be used instead.
net-im/ekg2:static - Link statically with plugins instead of installing them as shared libraries (external libraries can still be linked dynamically).
net-im/ekg2:web - Enable httprc_xajax WebUI plugin.
net-im/empathy:nautilus - Enable nautilus-sendto support
net-im/empathy:webkit - Build support for Adium-style HTML-based conversation window themes using net-libs/webkit-gtk
net-im/gajim:idle - Enable idle module
net-im/gajim:srv - SRV capabilities
net-im/gajim:trayicon - Enable support for trayicon
net-im/gajim:xhtml - Enable XHTML support
net-im/gnugadu:tlen - Enable Tlen.pl protocol support
net-im/gossip:debug - Enable debug path in gossip. net-libs/loudmouth needs to be compiled with USE="debug" to allow Gossip to actually build the debug code path.
net-im/gossip:galago - Enable desktop presence with galago
net-im/gossip:gnome-keyring - Allows Gossip to use gnome-keyring to store passwords.
net-im/gossip:libnotify - Allows Gossip to show visual notifications concerning various activities via libnotify.
net-im/jabberd2:memdebug - Enable nad and pool debug. Requires USE="debug" to be set. 
net-im/kadu:phonon - Enable phonon audio plugin
net-im/kadu:speech - Enables speech module
net-im/kmess:konqueror - Enable integration with konqueror
net-im/mcabber:aspell - Adds support for app-text/aspell spell checker.
net-im/mcabber:otr - Enable encrypted conversations using Off-The-Records messaging 
net-im/minbif:video - Add video support
net-im/pidgin:gadu - Enable Gadu Gadu protocol support
net-im/pidgin:groupwise - Enable Novell Groupwise protocol support
net-im/pidgin:gstreamer - Enables voice and video sessions
net-im/pidgin:gtk - Builds Pidgin, the GTK+ interface
net-im/pidgin:meanwhile - Enable meanwhile support for Sametime protocol
net-im/pidgin:ncurses - Build finch, console interface
net-im/pidgin:prediction - Enable Contact Availability Prediction plugin
net-im/pidgin:python - Build libgnt (GLib Ncurses Toolkit used by finch) with python scripting support
net-im/pidgin:qq - Enable QQ protocol support
net-im/pidgin:silc - Enable SILC protocol support
net-im/pidgin:xscreensaver - Use X screensaver protocol extension to monitor idle/active status based on mouse/keyboard events
net-im/pidgin:zephyr - Enable Zephyr protocol support
net-im/psi:enchant - Use enchant spell engine instead of aspell
net-im/psi:extras - Enables extra non official patches
net-im/psi:iconsets - Install additional iconsets, some of them has not clear licensing
net-im/psi:plugins - Enable plugins support
net-im/psi:powersave - Disable some non critical timers for much less CPU usage
net-im/psi:webkit - Enable chatlog rendering using webkit
net-im/psi:whiteboarding - Enable experimental interactive SVG drawing
net-im/psi:xscreensaver - Use X screensaver protocol extension to monitor idle/active status based on mouse/keyboard events
net-im/psimedia:demo -  build simple test application for the PsiMedia system. 
net-im/pyaim-t:webinterface - Install dependencies needed for the web interface 
net-im/pyicq-t:webinterface - Install dependencies needed for the web interface 
net-im/qutim:histman - Enable histman plugin
net-im/qutim:irc - Enable irc support
net-im/qutim:mrim - Enable mrim plugin
net-im/qutim:vkontakte - Enable vkontakte plugin
net-im/qutim:yandexnarod - Enable yanderx.narod plugin
net-im/skype:qt-static - Installs binaries statically linked to Qt
net-im/tkabber:extras - Enables extra non official patches
net-im/tkabber:plugins - Enables installation the extra plugins
net-irc/atheme:largenet - Enable support/tweaks for large networks
net-irc/bip:freenode - Enables freenode-specific functionality. Currently that is only support for mute lists (MODE #channel +q).
net-irc/bip:noctcp - Disable the automatic CTCP VERSION reply which is often exploited by malicious people to cause a DoS (reconnect due to flooding). 
net-irc/bip:oidentd - Enable oidentd support
net-irc/ezbounce:boost - Compile against dev-libs/boost libraries
net-irc/inspircd:openssl - Build dev-libs/openssl module
net-irc/kvirc:dcc_video - Support video connections over DCC protocol
net-irc/kvirc:dcc_voice - Support voice connections over DCC protocol
net-irc/kvirc:ipc - Support inter-process communication between KVIrc processes
net-irc/kvirc:phonon - Support Phonon for audio output
net-irc/kvirc:qt-dbus - Support Qt-DBus
net-irc/kvirc:qt-webkit - Support Qt-WebKit
net-irc/kvirc:transparency - Support pseudo-transparency
net-irc/ngircd:ident - Enables support for net-libs/libident
net-irc/psybnc:multinetwork - Adds support for multiple networks
net-irc/psybnc:oidentd - Adds support for oidentd
net-irc/psybnc:scripting - Adds scripting support
net-irc/quassel:X -  Build the Qt 4 GUI client for quassel. If this USE flag is disabled, the GUI is not built, and cannot be used. You might want to disable this on the server, but you need it enabled on the client. 
net-irc/quassel:ayatana -  Build in support for Ayatana notification using the libindicate-qt plugin. 
net-irc/quassel:crypt -  Support core->network per-channel and per-query blowfish encryption via app-crypt/qca:2. 
net-irc/quassel:monolithic -  Build Standalone client with integrated core, no external quasselcore needed. Only useful if you don't want to use quassels client/server model. The server and X flags are not needed in this case but it is possible to enable them too. 
net-irc/quassel:phonon -  Build client with phonon backend support. This enables sound playback in client. 
net-irc/quassel:server -  Build the server binary. If this USE flag is disabled, the 'core' server binary for quassel is not built, and cannot be used. You need this enabled on the server, but you might want to disable it on the client. 
net-irc/quassel:webkit -  Use qt-webkit rendering engine for showing URL thumbnails and for other things that need web browser integration. 
net-irc/rbot:aspell -  Use aspell instead of ispell in the "spell" plugin for rbot. The vanilla plugin uses ispell, but enabling this flag makes it use the ispell interface from aspell instead. 
net-irc/rbot:cal -  Add dependency over a package providing the /usr/bin/cal command, which is needed to enable the "cal" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:dict -  Add dependency over dev-ruby/ruby-dict, which is needed to enable the "dict" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:figlet -  Add dependency over app-misc/figlet, which is used by the "figlet" plugin for rbot. If the USE flag is disabled the plugin will be unable to use figlet; if toilet is also disabled, the plugin will be disabled. 
net-irc/rbot:fortune -  Add dependency over games-misc/fortune-mod, which is needed to enable the "fortune" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:host -  Add dependency over net-dns/bind-tools (providing /usr/bin/host), which is needed to enable the "host" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:hunspell -  Use hunspell instead of ispell in the "spell" plugin for rbot. The vanilla plugin uses ispell, but enabling this flag makes it use the ispell interface from hunspell instead. It's overridden by the aspell USE flag. For native hunspell support check the rbot-hunspell plugin. 
net-irc/rbot:nls -  Build and install translation for the messages coming from the bot and its plugins (through dev-ruby/ruby-gettext). 
net-irc/rbot:shorturl -  Add dependency over dev-ruby/shorturl, which is needed to enable the "shortenurl" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:timezone -  Add dependency over dev-ruby/tzinfo to enable the "time" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/rbot:toilet -  Add dependency over app-misc/toilet, which is used by the "figlet" plugin for rbot. If the USE flag is disabled the plugin will be unable to use toilet; if figlet is also disabled, the plugin will be disabled. 
net-irc/rbot:translator -  Add dependency over dev-ruby/mechanize, which is needed to enable the "translator" plugin for rbot. If the USE flag is disabled the plugin is also disabled by default. 
net-irc/srvx:bahamut - Choose bahamut protocol over p10 protocol
net-irc/supybot:twisted - Allows supybot to use dev-python/twisted as driver
net-irc/unrealircd:hub - Enable hub support
net-irc/unrealircd:operoverride - Enable OperOverride extension
net-irc/unrealircd:operoverride-verify - Enable requiring opers to invite themselves to +s/+p channels
net-irc/unrealircd:prefixaq - Enable chanadmin and chanowner prefixes
net-irc/unrealircd:showlistmodes - Support displaying channel modes in /list
net-irc/unrealircd:shunnotices - Enable notifying a user when un-shunned
net-irc/unrealircd:spoof - Enable the spoof protection
net-irc/unrealircd:topicisnuhost - Enable displaying nick!user@host as topic setter
net-irc/unrealircd:usermod - Enable /set* and /chg* commands
net-irc/weechat:alias - Enable plugin for alias control.
net-irc/weechat:charset - Enable encoding conversions.
net-irc/weechat:fifo - Enable FIFO support (sh pipes).
net-irc/weechat:gtk - Enable (experimental) gtk interface.
net-irc/weechat:irc - Enable IRC protocol support.
net-irc/weechat:logger - Enable support for logging.
net-irc/weechat:relay - Enable relay plugin (experimental)
net-irc/weechat:rmodifier - Enable rmodifier plugin.
net-irc/weechat:scripts - Build infrastructure for scripting.
net-irc/weechat:xfer - Enable xfer plugin support.
net-irc/xchat:ntlm - Enable NTLM authentication
net-irc/xchat:xchatdccserver - Enables support for the /dccserver command via a patch
net-irc/xchat:xchatnogtk - Disables building the GTK front end to XChat
net-irc/xchat-gnome:sound - Enable sound event support with media-libs/libcanberra
net-irc/xchat-xsys:audacious - Enables media-sound/audacious integration
net-irc/znc:ares - Enables support for asynchronous DNS using the c-ares library
net-irc/znc:extras - Enable some additional modules
net-libs/aqbanking:chipcard - Enable support for DDV/RSA-chipcards
net-libs/c-client:doc - Install RFCs related to IMAP
net-libs/clinkcc:mythtv - Enable MythTV support
net-libs/courier-authlib:vpopmail - Enable vpopmail support
net-libs/cvm:vpopmail - Enable vpopmail support
net-libs/daq:afpacket - Build the AFPacket data acquisition module
net-libs/daq:dump - Build the Dump data acquisition module
net-libs/daq:pcap - Build the PCAP data acquisition module
net-libs/farsight2:upnp - Enable UPnP IGD support
net-libs/gnutls:nettle - Use dev-libs/nettle as crypto backend
net-libs/gnutls:valgrind - Enable testing using dev-util/valgrind.
net-libs/gssdp:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/gtk-vnc:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/gupnp:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/gupnp-av:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/iax:snomhack - Use slower memset for SNOM phoneem
net-libs/ldns:gost - Enable GOST support
net-libs/libeXosip:srv - enable support for SRV records DNS queries
net-libs/libesmtp:ssl -  Enable support for advanced SMTP authentication methods, like NTML and STARTTLS. Also use OpenSSL's MD5 implementation over internal version. 
net-libs/libetpan:liblockfile - Enable support for liblockfile library
net-libs/libfwbuilder:bind - Use bind's name resolving library
net-libs/libfwbuilder:stlport - Enagle support for STLport
net-libs/libinfinity:server -  Build and install the server binary including init.d/conf.d-scripts. Needed if you want to host an infinote server for gobby. 
net-libs/libmicrohttpd:messages - enable error messages
net-libs/libnice:upnp - Enable UPnP IGD support
net-libs/libnids:glib - Use dev-libs/glib for multiprocessing support
net-libs/libnids:libnet - Include code requiring net-libs/libnet
net-libs/liboauth:bindist -  Alias for the nss USE flag, since there are license compliancy trouble when using OpenSSL. 
net-libs/liboauth:curl -  If enabled, net-misc/curl is used thorugh the libcurl library; if it's not, the curl command is used instead. Some features are only available when using the library, but using it as library requires matching SSL implementations. 
net-libs/liboauth:nss -  Use Mozilla NSS (dev-libs/nss) as hash library; if this is disabled, dev-libs/openssl is used instead. 
net-libs/libpcap:libnl - link with dev-libs/libnl (used to put wireless interfaces in monitor mode)
net-libs/libpri:bri - Enable ISDN BRI support (bristuff)
net-libs/libproxy:gnome - Enable support for reading proxy settings from GNOME using gnome-base/gconf
net-libs/libproxy:kde - Enable support for reading proxy settings from KDE
net-libs/libproxy:vala - Enable support for the Vala programming language
net-libs/libproxy:webkit - Enable support for reading proxy settings from net-libs/webkit-gtk
net-libs/libproxy:xulrunner - Enable support for reading proxy settings from net-libs/xulrunner
net-libs/libsoup:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/libsoup-gnome:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/libsrtp:aesicm - Use AES ICM cryptographic algorithm
net-libs/libsrtp:console -  Use /dev/console instead of stdout for error messages 
net-libs/libsrtp:syslog - Use syslog for error messages
net-libs/libssh:gcrypt - Prefer dev-libs/libgcrypt over dev-libs/openssl for encryption
net-libs/libssh:server - Build with SSH server support
net-libs/libssh:sftp - Build with SFTP support
net-libs/libssh:ssh1 - Build with SSH1 support
net-libs/libssh2:gcrypt - Use dev-libs/libgcrypt for crypto
net-libs/libvncserver:no24bpp - disable 24bpp support
net-libs/loudmouth:asyncns - Use libasyncns for asynchronous name resolution.
net-libs/neon:libproxy - Add support for net-libs/libproxy
net-libs/neon:pkcs11 - Add support for PKCS#11 using dev-libs/pakchois
net-libs/netembryo:sctp - Support for Stream Control Transmission Protocol
net-libs/opal:audio - Enable audio support
net-libs/opal:capi - Enable CAPI support
net-libs/opal:celt - Enable CELT ultra-low delay audio codec
net-libs/opal:dtmf - Enable DTMF encoding/decoding support
net-libs/opal:fax - Enable T.38 FAX protocol
net-libs/opal:h224 - Enable H.224 real time control protocol
net-libs/opal:h281 - Enable H.281 Far-End Camera Control protocol
net-libs/opal:h323 - Enable H.323 protocol
net-libs/opal:iax - Enable Inter-Asterisk eXchange protocol
net-libs/opal:ivr - Enable Interactive Voice Response
net-libs/opal:ixj - Enable xJack cards support
net-libs/opal:lid - Enable Line Interface Device
net-libs/opal:noaudio - Disable audio codecs
net-libs/opal:novideo - Disable video codecs
net-libs/opal:plugins - Enable plugins support
net-libs/opal:sbc - Enable the Bluetooth low-complexity, SubBand Codec 
net-libs/opal:sip - Enable Session Initiation Protocol
net-libs/opal:sipim - Enable SIP Instant Messages session
net-libs/opal:srtp - Enable Secure Real-time Transport Protocol
net-libs/opal:stats - Enable statistic reporting
net-libs/opal:swig - Use swig to generate bindings
net-libs/opal:video - Enable video support
net-libs/opal:vpb - Enable Voicetronics VPB card support
net-libs/opal:vxml - Enable VXML support
net-libs/opal:wav - Enable WAVFILE support
net-libs/opal:x264-static - Install x264 plugin statically linked with x264 
net-libs/openh323:noaudio - Disable audio codecs
net-libs/openh323:novideo - Disable video codecs
net-libs/ortp:srtp - Add support for Secure RTP
net-libs/pjsip:epoll - epoll system call support
net-libs/pjsip:ext-sound - External sound device support
net-libs/pjsip:g711 - Builds the G711 codec
net-libs/pjsip:g722 - Builds the G722 codec
net-libs/pjsip:g7221 - Builds the G7221 codec
net-libs/pjsip:ilbc - Builds the ilbc codec
net-libs/pjsip:l16 - Builds the L16 codec
net-libs/ptlib:asn - Enable ASN decoding/encoding support
net-libs/ptlib:audio - Enable audio support
net-libs/ptlib:dtmf - Enable DTMF encoding/decoding support
net-libs/ptlib:http - Enable HTTP support
net-libs/ptlib:mail - Enable mail protocols (POP3/SMTP)
net-libs/ptlib:qos - Enable QOS support
net-libs/ptlib:remote - Enable remote connection support
net-libs/ptlib:serial - Enable serial port support
net-libs/ptlib:shmvideo - Enable shared memory video devices
net-libs/ptlib:socks - Enable SOCKS protocol support
net-libs/ptlib:stun - Enable STUN support
net-libs/ptlib:telnet - Enable telnet protocol support
net-libs/ptlib:tts - Enable Text-To-Speech server support
net-libs/ptlib:video - Enable video support
net-libs/ptlib:vxml - Enable VoiceXML support
net-libs/ptlib:wav - Enable WAVFILE support
net-libs/telepathy-glib:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/telepathy-glib:vala - Enable bindings for dev-lang/vala
net-libs/webkit-gtk:coverage - enable code coverage support
net-libs/webkit-gtk:introspection - Use dev-libs/gobject-introspection for introspection
net-libs/webkit-gtk:websockets - enable full duplex single socket communication
net-libs/wt:extjs - Build Wt Ext library with JavaScript-only widgets (http://extjs.com/)
net-libs/wt:fcgi - Compile in FCGI connector
net-libs/wt:graphicsmagick - Enable GraphicsMagick, for supporting painting to raster images (PNG, GIF, ...) (WRasterImage)
net-libs/wt:resources - Install resources directory
net-libs/wt:server - Compile in stand-alone httpd connector
net-libs/xulrunner:custom-optimization - Fine-tune custom compiler optimizations
net-libs/xulrunner:ipc - Use inter-process communication between tabs and plugins. Allows for greater stability in case of plugin crashes
net-libs/xulrunner:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
net-libs/zeromq:pgm -  0MQ is build with 'Pragmatic General Multicast' (RFC 3208) support using the excellent OpenPGM implementation. 
net-mail/courier-imap:trashquota - include deleted messages, and the Trash folder, in the estimated quota usage for maildirs
net-mail/cyrus-imapd:idled - Enable idled vs poll IMAP IDLE method
net-mail/cyrus-imapd:replication - Enable replication support in the cyrus imap server
net-mail/cyrus-imapd:sieve - Enable sieve support
net-mail/dbmail:sieve - Enable sieve filter support
net-mail/dovecot:cydir - Add cydir storage support
net-mail/dovecot:dbox - Add dbox storage support
net-mail/dovecot:managesieve - Add managesieve protocol support
net-mail/dovecot:mdbox - Add mdbox storage support
net-mail/dovecot:pop3d - Add pop3d support
net-mail/dovecot:sdbox - Add sdbox storage support
net-mail/dovecot:sieve - Add sieve support
net-mail/dovecot:vpopmail - Add vpopmail support
net-mail/fdm:courierauth - Add support for Courier authentication library
net-mail/fetchmail:hesiod - Enable support for hesiod
net-mail/fetchmail:tk - Adds support for Tk GUI toolkit, in particular it installs fetchmailconf
net-mail/gnubiff:password - Enable save passwords to connect mail servers in user space
net-mail/hotwayd:smtp - Build SMTP proxy (hotsmtpd)
net-mail/lbdb:abook - Enables app-misc/abook support
net-mail/lbdb:finger - Enables finger support
net-mail/libpst:dii - enable dii support
net-mail/mailutils:tokyocabinet - Enable Tokyo Cabinet database support
net-mail/mairix:gnus - Add support for the marks propagation feature in app-emacs/gnus
net-mail/qmailadmin:maildrop - Filter spam using maildrop
net-mail/qpopper:apop - Enables the pop.auth file in /etc/pop.auth
net-mail/qpopper:drac - Enables DRAC support
net-mail/qpopper:mailbox - Enables mail spool file is in home directory ~/Mailbox
net-mail/teapop:virtual - Enable teapop's virtual domain support.
net-mail/tpop3d:authexternal - Enable authentication by an external program
net-mail/tpop3d:drac - Enable dynamic relay support in the tpop3d pop3 server
net-mail/tpop3d:flatfile - Enable authentication against /etc/passwd-style flat files
net-mail/tpop3d:passwd - Enable /etc/passwd authentication
net-mail/tpop3d:sha1 - Use OpenSSL for sha1 encrypted passwords.
net-mail/tpop3d:shadow - Enable /etc/shadow authentication
net-mail/uw-imap:clearpasswd - Enables cleartext logins outside of SSL sessions
net-mail/vchkuser:debug - Enables debug messages to syslog
net-mail/vpopmail:clearpasswd - Enables cleartext password storage in the vpasswd files
net-mail/vpopmail:ipalias - Enables enable-ip-alias-domains
net-mail/vpopmail:maildrop - Enables mail-filter/maildrop support in vdelivermail
net-mail/vpopmail:spamassassin - Enables mail-filter/spamassassin support
net-misc/aria2:ares - Enables support for asynchronous DNS using the c-ares library
net-misc/aria2:bittorrent - Enables support for the bittorrent protocol
net-misc/aria2:metalink - Enables support for metalink
net-misc/aria2:scripts - Install additional scripts which use aria2's xmlrpc functionality
net-misc/asterisk:ais - Support clustering using the Application Interface Specification framework
net-misc/asterisk:dahdi - Support Digium compatible hardware (formerly known as Zaptel).
net-misc/asterisk:gtalk - Enable support for Google Talk services
net-misc/asterisk:h323 - Enable support for the H323 telephony protocol
net-misc/asterisk:http - Enable embedded web server
net-misc/asterisk:keepsrc - Install sources into /usr/src for custom patching
net-misc/asterisk:logrotate - Install a configuration snippet for the logrotate cronjob
net-misc/asterisk:lowmem - Build Asterisk for environments with low amounts of memory (embedded devices)
net-misc/asterisk:misdn - Build with mISDN (chan_misdn) support for BRI ISDN cards
net-misc/asterisk:newt - Include additional tools that require redhats windowing toolkit
net-misc/asterisk:nosamples - Don't install sample sound and configuration files
net-misc/asterisk:osp - Enable support for the Open Settlement Protocol
net-misc/asterisk:osplookup - Support secure peering using the Open Settlement Protocol
net-misc/asterisk:pri - Enables pri support
net-misc/asterisk:samples - Install sample sound and configuration files (default: on)
net-misc/asterisk:span - Enable support for the spandsp codec
net-misc/asterisk:srtp - Enable support for encrypted voice transmission (secure RTP)
net-misc/asterisk:zaptel - Enables deprecated zaptel support (use dahdi if available)
net-misc/asterisk-addons:h323 - Build the chan_ooh323c H.323 channel driver
net-misc/asterisk-core-sounds:alaw - Install the sounds files for the alaw codec.
net-misc/asterisk-core-sounds:g722 - Install the sounds files for the g722 codec.
net-misc/asterisk-core-sounds:g729 - Install the sounds files for the g729 codec.
net-misc/asterisk-core-sounds:gsm - Install the sounds files for the +gsm codec.
net-misc/asterisk-core-sounds:siren14 - Install the sounds files for the siren14 codec.
net-misc/asterisk-core-sounds:siren7 - Install the sounds files for the siren7 codec.
net-misc/asterisk-core-sounds:sln16 - Install the sounds files for the sln16 codec.
net-misc/asterisk-core-sounds:ulaw - Install the sounds files for the ulaw codec.
net-misc/asterisk-core-sounds:wav - Install the sounds files for the wav codec.
net-misc/asterisk-extra-sounds:alaw - Install the sounds files for the alaw codec.
net-misc/asterisk-extra-sounds:g722 - Install the sounds files for the g722 codec.
net-misc/asterisk-extra-sounds:g729 - Install the sounds files for the g729 codec.
net-misc/asterisk-extra-sounds:gsm - Install the sounds files for the +gsm codec.
net-misc/asterisk-extra-sounds:siren14 - Install the sounds files for the siren14 codec.
net-misc/asterisk-extra-sounds:siren7 - Install the sounds files for the siren7 codec.
net-misc/asterisk-extra-sounds:sln16 - Install the sounds files for the sln16 codec.
net-misc/asterisk-extra-sounds:ulaw - Install the sounds files for the ulaw codec.
net-misc/asterisk-extra-sounds:wav - Install the sounds files for the wav codec.
net-misc/asterisk-moh-opsound:alaw - Install the sounds files for the alaw codec.
net-misc/asterisk-moh-opsound:g722 - Install the sounds files for the g722 codec.
net-misc/asterisk-moh-opsound:g729 - Install the sounds files for the g729 codec.
net-misc/asterisk-moh-opsound:gsm - Install the sounds files for the +gsm codec.
net-misc/asterisk-moh-opsound:siren14 - Install the sounds files for the siren14 codec.
net-misc/asterisk-moh-opsound:siren7 - Install the sounds files for the siren7 codec.
net-misc/asterisk-moh-opsound:sln16 - Install the sounds files for the sln16 codec.
net-misc/asterisk-moh-opsound:ulaw - Install the sounds files for the ulaw codec.
net-misc/asterisk-moh-opsound:wav - Install the sounds files for the wav codec.
net-misc/cfengine:html - Install HTML documentation
net-misc/cfengine:libvirt - Enable support for virtual machine management through app-emulation/libvirt
net-misc/cfengine:mysql - Use dev-db/mysql as database backend, default would be Berkeley DB (sys-libs/db)
net-misc/cfengine:pcre - Use PCRE rather than GNU Regex from libc
net-misc/cfengine:postgres - Use dev-db/postgresql-server as database backend, default would be Berkeley DB (sys-libs/db)
net-misc/cfengine:qdbm - Use dev-db/qdbm as database backend, default would be Berkeley DB (sys-libs/db)
net-misc/cfengine:tests - Install test files
net-misc/cfengine:tokyocabinet - Use dev-db/tokyocabinet as database backend, default would be Berkeley DB (sys-libs/db)
net-misc/connman:dhclient - Use dhclient from net-misc/dhcp for getting ip.
net-misc/connman:dnsproxy - Enable dnsproxy support.
net-misc/connman:ethernet - Enable ethernet support.
net-misc/connman:google - Enable Google Public DNS support.
net-misc/connman:ofono - Use net-misc/ofono for telephony support.
net-misc/connman:openvpn - Use net-misc/openvpn for openvpn support.
net-misc/connman:tools - Enable testing tools.
net-misc/connman:wimax - Use net-wireless/wimax for WiMAX support.
net-misc/curl:ares - Enabled c-ares dns support
net-misc/curl:gnutls - Prefer gnutls over nss and openssl as the crypto engine
net-misc/curl:libssh2 - Enabled SSH urls in curl using libssh2
net-misc/curl:nss - Prefer NSS over openssl as the crypto engine
net-misc/curl:ssl - Enable crypto engine support (via openssl if USE='-gnutls -nss')
net-misc/dahdi:flash - Support (short) flash on FXS
net-misc/dahdi-tools:ppp - Enables PPP/DAHDIRAS support
net-misc/dhcpcd:compat - Enable commandline compatibility with dhcpcd-3.x
net-misc/directvnc:mouse - Adds mouse support
net-misc/dnetstats:gnome - Use gksu to gain root access
net-misc/dnetstats:kde - Use kdesu to gain root access
net-misc/dropbear:bsdpty - Add support for legacy BSD pty's rather than dynamic UNIX pty's -- do not use this flag unless you are absolutely sure you actually want it
net-misc/dropbear:multicall - Build all the programs as one little binary (to save space)
net-misc/gwget:epiphany - Build epiphany extensions
net-misc/htbinit:esfq - Add support for Enhanced Stochastic Fairness queueing discipline.
net-misc/hylafax:html - Adds HTML documentation
net-misc/hylafax:mgetty - Adds support for mgetty and vgetty
net-misc/icecast:yp - Build support for yp public directory listings
net-misc/iputils:SECURITY_HAZARD - Allow non-root users to flood (ping -f). This is generally a very bad idea.
net-misc/italc:system-libvncserver - Build against the system libvncserver (experimental)
net-misc/knock:server - Installs the knockd server daemon.
net-misc/mediatomb:inotify - Enable inotify filesystem monitoring support
net-misc/mediatomb:lastfm - Enable last.fm support
net-misc/mediatomb:libextractor - Use libextractor to gather files' metadata.
net-misc/mediatomb:mysql - Use dev-db/mysql as backend rather than SQLite3. If this USE flag is disabled, dev-db/sqlite is used instead.
net-misc/mediatomb:taglib - Use media-libs/taglib for reading files' metadata rather than id3lib. If this USE flag is disabled media-libs/id3lib is used instead.
net-misc/mediatomb:thumbnail - Enables video thumbnails generation through media-video/ffmpegthumbnailer
net-misc/memcached:slabs-reassign - Allow manual reassignment of memory slabs at the cost of slab optimizations.
net-misc/networkmanager:connection-sharing - Use net-dns/dnsmasq and net-firewall/iptables for connection sharing 
net-misc/networkmanager:dhclient - Use dhclient from net-misc/dhcp for getting ip.
net-misc/networkmanager:dhcpcd - Use net-misc/dhcpcd for getting ip.
net-misc/networkmanager:nss - Use dev-libs/nss for cryptography.
net-misc/networkmanager:resolvconf - Use net-dns/openresolv for managing DNS information
net-misc/ntp:openntpd - Allow ntp to be installed alongside openntpd
net-misc/ntp:parse-clocks - Add support for PARSE clocks
net-misc/nxcl:nxclient - Use nxssh from net-misc/nxclient instead of standard ssh
net-misc/nxserver-freenx:nxclient - Allow to install net-misc/nxclient in parallel with this package, using it to display messages in the sessions
net-misc/ofono:atmodem - ETSI AT modem support.
net-misc/ofono:isimodem - Enable PhoNet/ISI modem support.
net-misc/oidentd:masquerade - Enable support for masqueraded/NAT connections
net-misc/openssh:X509 - Adds support for X.509 certificate authentication
net-misc/openssh:hpn - Enable high performance ssh
net-misc/openssh:ldap - Add support for storing SSH public keys in LDAP
net-misc/openssh:pkcs11 - Enable PKCS#11 smartcard support
net-misc/openswan:curl - Include curl support (used for fetching CRLs)
net-misc/openswan:extra-algorithms - Include additional strong algorithms (Blowfish, Twofish, Serpent and SHA2)
net-misc/openswan:ldap - Include LDAP support (used for fetching CRLs)
net-misc/openswan:ms-bad-proposal - Allow bad IP address proposal offered by an Microsoft L2TP/IPSec servers
net-misc/openswan:nocrypto-algorithms - Include algorithms that don't even encrypt (1DES)
net-misc/openswan:nss - Include libnss support (adds smartcard support)
net-misc/openswan:ssl - Use OpenSSL libraries for BIGNUM support
net-misc/openswan:weak-algorithms - Include weak algorithms (DH1)
net-misc/openvpn:eurephia - Apply eurephia patch
net-misc/openvpn:iproute2 - Enabled iproute2 support instead of net-tools
net-misc/openvpn:passwordsave - Enables openvpn to save passwords
net-misc/openvpn:pkcs11 - Enable PKCS#11 smartcard support
net-misc/pino:indicate - Use dev-libs/libindicate to notify other apps
net-misc/plowshare:view-captcha - View captcha with aview
net-misc/quagga:bgpclassless -  Apply unofficial patch to enable classless prefixes for BGP. Patch and information to be found at http://hasso.linux.ee/doku.php/english:network:quagga 
net-misc/quagga:multipath -  Enable multipath routes support for any number of routes 
net-misc/quagga:ospfapi -  Enable OSPFAPI support for client applications accessing the OSPF link state database 
net-misc/quagga:pam -  Add support for PAM (viasys-libs/pam) to the Quagga Virtual Terminal Interface Shell (vtysh); if the readline USE flag is disabled, this flag is ignored. 
net-misc/quagga:readline -  Enable support for sys-libs/readline to provide the Quagga Virtual Terminal Interface Shell (vtysh). 
net-misc/quagga:realms -  Apply unofficial patch to enable realms support. Patch and information to be found at http://vcalinus.gemenii.ro/quaggarealms.html and http://linux.mantech.ro/quagga+realm_en.php 
net-misc/quagga:tcp-zebra -  Enable TCP zserv interface on port 2600 for Zebra/protocol-daemon communication. Unix domain sockets are chosen otherwise. 
net-misc/rdesktop:pcsc-lite - Enable smartcard support with sys-apps/pcsc-lite driver
net-misc/rdesktop:rdpusb - Enable USB redirection support for app-emulation/virtualbox-bin
net-misc/remmina:ssh - Enable support for SSH/SFTP using net-libs/libssh
net-misc/remmina:unique - Enable single instance support using dev-libs/libunique
net-misc/remmina:vte - Enable Terminal support using x11-libs/vte
net-misc/remmina:xdmcp - Enable support for X Display Manager Control Protocol
net-misc/rygel:tracker - Install dependencies for the tracker plugin
net-misc/rygel:transcode - Install dependencies for transcoding support
net-misc/scponly:gftp - Enables gFTP compatibility
net-misc/scponly:logging - Enables SFTP logging compatibility
net-misc/scponly:passwd - Enables passwd compatibility
net-misc/scponly:quota - Enables quota compatibility
net-misc/scponly:rsync - Enables rsync compatibility with potential security risks
net-misc/scponly:scp - Enables scp compatibility with potential security risks
net-misc/scponly:sftp - Enables SFTP compatibility
net-misc/scponly:subversion - Enables Subversion compatibility with potential security risks
net-misc/scponly:unison - Enables Unison compatibility with potential security risks
net-misc/scponly:wildcards - Enables wildcard processing with potential security risks
net-misc/scponly:winscp - Enables WinSCP 2.0 compatibility with potential security risks
net-misc/sitecopy:rsh - This allows the use of rsh (remote shell) and rcp (remote copy) for authoring websites. sftp is a much more secure protocol and is preferred.
net-misc/sitecopy:webdav - Enable WebDav (Web-based Distributed Authoring and Versioning) support. This system allows users to collaborate on websites using a web based interface. See the ebuild for an FAQ page. Enables neon as well to handle webdav support.
net-misc/slimrat:X - Install also GUI client
net-misc/streamtuner:shout - Enable shoutcast plug-in.
net-misc/streamtuner:xiph - Enable xiph.org plug-in.
net-misc/strongswan:cisco -  Enable support for the Cisco VPN client. 
net-misc/strongswan:dhcp -  Enable server support for querying virtual IP addresses for clients from a DHCP server. (IKEv2 only) 
net-misc/strongswan:eap -  Enable support for the different EAP modules that is supported. 
net-misc/strongswan:farp -  Enable faking of ARP responses for virtual IP addresses assigned to clients. (IKEv2 only) 
net-misc/strongswan:gcrypt -  Enable dev-libs/libgcrypt plugin which provides 3DES, AES, Blowfish, Camellia, CAST, DES, Serpent and Twofish ciphers along with MD4, MD5 and SHA1/2 hash algorithms, RSA and DH groups 1,2,5,14-18 and 22-24(4.4+). Also includes a software random number generator. 
net-misc/strongswan:ikev1 -  Enable IKEv1 protocol (pluto daemon). 
net-misc/strongswan:ikev2 -  Enable IKEv2 protocol (charon daemon). 
net-misc/strongswan:nat-transport -  Enable potentially insecure NAT traversal for transport mode in IKEv1. Only enable if you really need this. 
net-misc/strongswan:non-root -  Force IKEv1/IKEv2 daemons to normal user privileges. This might impose some restrictions mainly to the IKEv1 daemon. Disable only if you really require superuser privileges. 
net-misc/strongswan:openssl -  Enable dev-libs/openssl plugin which is required for Elliptic Curve Cryptography (DH groups 19-21,25,26) and ECDSA. Also provides 3DES, AES, Blowfish, Camellia, CAST, DES, IDEA and RC5 ciphers along with MD2, MD4, MD5 and SHA1/2 hash algorithms, RSA and DH groups 1,2,5,14-18 and 22-24(4.4+) dev-libs/openssl has to be compiled with USE="-bindist". 
net-misc/stunnel:xforward - Enable X-Forwarded-For support for Stunnel
net-misc/termpkg:uucp -  Adds support for uucp style device locking 
net-misc/tigervnc:server - Build TigerVNC server
net-misc/tigervnc:xorgmodule - Build the Xorg module
net-misc/tightvnc:server - Build vncserver. Allows us to only build server on one machine if set, build only viewer otherwise.
net-misc/vde:pcap -  Enable the pcap-based plugin that allows creating a switch against a real interface. 
net-misc/vde:ssl -  Enable the cryptcab plugin that allows creating an encrypted virtual cable. 
net-misc/vidalia:tor - Allow to use a local tor setup
net-misc/vinagre:applet - Enable vinagre applet for gnome-base/gnome-panel.
net-misc/vinagre:ssh - Enable ssh plugin.
net-misc/vinagre:telepathy - Enable access to remote desktop via a telepathy client.
net-misc/vino:telepathy - Enable desktop sharing through a telepathy client
net-misc/vpnc:hybrid-auth - Enable hybrid authentication (certificates), only if not redistributed as compiled binary
net-misc/vpnc:resolvconf - Enable support for DNS managing framework net-dns/openresolv
net-misc/wget:ntlm - Enable support for NTLM (Windows-based) authorization
net-misc/wicd:gtk - Installs a gtk UI. This is enabled by default because it is intended behavior. Requires dev-python/pygtk
net-misc/wicd:ioctl - Installs additional python libraries to use as a backend. This will improve speed but is experimental.
net-misc/wicd:ncurses - Installs a ncurses UI
net-misc/wicd:pm-utils - Installs the pm-utils hooks for suspend/resume and requires sys-power/pm-utils
net-misc/x2goserver:fuse - Use sys-fs/sshfs-fuse to allow shared folders
net-misc/yaydl:soundextract - Extract the soundtracks of the downloaded videos
net-misc/zaptel:astribank - Install Xorcom Astribank utilities
net-misc/zaptel:bri - Enable ISDN BRI support (bristuff)
net-misc/zaptel:ecaggressive - Make the mark2 echo canceller a little more aggressive
net-misc/zaptel:eckb1 - Use the KB1 echo canceller
net-misc/zaptel:ecmark - Use the MARK echo canceller
net-misc/zaptel:ecmark2 - Use the MARK2 echo canceller (default)
net-misc/zaptel:ecmark3 - Use the MARK3 echo canceller
net-misc/zaptel:ecmg2 - Use the MG2 echo canceller
net-misc/zaptel:ecsteve - Use the STEVE echo canceller
net-misc/zaptel:ecsteve2 - Use the STEVE2 echo canceller
net-misc/zaptel:florz - Enable florz enhancement patches for ISDN BRI
net-misc/zaptel:rtc - Use the realtime clock on x86 and amd64 systems instead of kernel timers
net-misc/zaptel:watchdog - Enable the watchdog to monitor unresponsive and misbehaving interfaces
net-misc/zaptel:zapnet - Enable SyncPPP, CiscoHDLC and Frame-Relay support
net-misc/zaptel:zapras - Enable PPP support for Remote-Access-Service
net-nds/389-ds-base:auto-dn-suffix - Enable auto bind with auto dn suffix over unix domain socket (LDAPI) support
net-nds/389-ds-base:autobind - Enable auto bind over unix domain socket (LDAPI) support
net-nds/389-ds-base:bitwise - Enable bitwise plugin - supported data in raw/bitwise format
net-nds/389-ds-base:dna - Enable dna (distributed numeric assignment ) plugin - to automatically assign unique uid numbers to new user entries as they are created.
net-nds/389-ds-base:ldapi - Enable LDAP over unix domain socket (LDAPI) support
net-nds/389-ds-base:pam-passthru - Enable pam-passthru plugin - for simple and fast system services used in ldap
net-nds/389-ds-base:presence - Enable presence plugin - non-stabdart syntax validation
net-nds/gosa-core:mail - Manage mail accounts and servers with gosa.
net-nds/gosa-core:samba - Manage samba accounts with gosa.
net-nds/nsscache:nsscache - Depend on sys-auth/libnss-cache to handle flat files
net-nds/nsscache:nssdb - Depend on sys-libs/libnss_db to handle dbm files.
net-nds/openldap:experimental - Enable experimental backend options
net-nds/openldap:odbc - Enable ODBC and SQL backend options
net-nds/openldap:overlays - Enable contributed OpenLDAP overlays
net-nds/openldap:smbkrb5passwd - Enable overlay for syncing ldap, unix and lanman passwords
net-nds/tac_plus:finger - Adds support for checking user counts via fingering the NAS
net-news/liferea:dbus -  Enables the DBUS connector for liferea, so feeds can be managed from external programs 
net-news/liferea:gnutls -  Enable https feeds using gnutls 
net-news/liferea:gtkhtml -  Uses the gtkhtml rendering engine for item rendering. Deprecated, and broken on amd64. 
net-news/liferea:libnotify -  Enable popup notifications 
net-news/liferea:lua -  Enable lua scripting 
net-news/liferea:networkmanager -  Enable NetworkManager integration to automatically detect online/offline status 
net-news/liferea:webkit -  Enable the webkit rendering engine for item rendering 
net-news/liferea:xulrunner -  Enable the xulrunner 1.9 rendering engine for item rendering 
net-nntp/inn:innkeywords - Enable automatic keyword generation support
net-nntp/inn:inntaggedhash - Use tagged hash table for history (disables large file support)
net-nntp/nzbget:parcheck - Enable support for checking PAR archives
net-nntp/slrn:uudeview - Add support for yEnc coding and more using dev-libs/uulib
net-nntp/tin:cancel-locks - Enable Cancel-Lock header functionality (also enables USE=evil)
net-nntp/tin:etiquette - Enable the display off posting etiquettes
net-nntp/tin:evil - Let tin generate a message ID
net-nntp/tin:forgery - Cancel messages posted from a different account
net-p2p/amule:daemon - Enable amule daemon
net-p2p/amule:remote - Enable remote controlling of the client
net-p2p/amule:stats - Enable statistic reporting
net-p2p/amule:upnp - Enables support for Intel UPnP stack.
net-p2p/dbhub:switch_user - Enable support for switching user
net-p2p/deluge:webinterface - Install dependencies needed for the web interface 
net-p2p/eiskaltdcpp:emoticons - Install emoticon packs
net-p2p/eiskaltdcpp:sounds - Install sound files
net-p2p/eiskaltdcpp:upnp - Forward ports using UPnP
net-p2p/fms:frost - Add support for frost boards
net-p2p/freenet:freemail - Add Freemail support
net-p2p/gift:ares - pull in Ares plugin
net-p2p/gift:fasttrack - pull in FastTrack plugin
net-p2p/gift:gnutella - pull in Gnutella plugin
net-p2p/gift:openft - pull in OpenFT plugin
net-p2p/ktorrent:bwscheduler - Schedule upload and download limits over a period of a week
net-p2p/ktorrent:downloadorder - Specify the download order of a multi-file torrent
net-p2p/ktorrent:infowidget - Displays general information about a torrent in several tabs
net-p2p/ktorrent:ipfilter - Filter IP addresses through a blocklist
net-p2p/ktorrent:kross - Enable kross scripting support
net-p2p/ktorrent:logviewer - Displays the logging output
net-p2p/ktorrent:magnetgenerator - Generates magnet URI's
net-p2p/ktorrent:mediaplayer - Phonon-based media player
net-p2p/ktorrent:rss - Syndication plugin for KTorrent, supporting RSS and Atom feeds
net-p2p/ktorrent:scanfolder - Scan folders for torrent files and load them
net-p2p/ktorrent:search - Search for torrents
net-p2p/ktorrent:shutdown - Shutdown when done
net-p2p/ktorrent:stats - Shows statistics about torrents in several graphs
net-p2p/ktorrent:upnp - Forward ports using UPnP
net-p2p/ktorrent:webinterface - Allows control of KTorrent via a web interface
net-p2p/ktorrent:zeroconf - Discover peers on the local network using the Zeroconf protocol
net-p2p/mktorrent:largefile - Enable largefile support on 32 bit systems
net-p2p/mldonkey:bittorrent - enable bittorrent support
net-p2p/mldonkey:fasttrack - enable fasttrack support
net-p2p/mldonkey:gnutella - enable gnutella and gnutella2 support
net-p2p/mldonkey:guionly - enable client build only
net-p2p/mldonkey:magic - enable use of libmagic
net-p2p/rtorrent:daemon - Uses app-misc/screen to daemonize this application 
net-p2p/transmission:sound - Enable sound event support with media-libs/libcanberra
net-print/hplip:X - Enables scanner GUI dependencies with USE="scanner" where media-gfx/xsane is preferred over media-gfx/sane-frontends
net-print/hplip:doc - Build documentation
net-print/hplip:fax - Enable fax on multifunction devices which support it
net-print/hplip:hpcups - Build the hpcups driver for cups (by HP)
net-print/hplip:hpijs - Build the IJS driver for cups (Foomatic)
net-print/hplip:kde - Enables kde-misc/skanlite as scanner GUI with USE="scanner X"
net-print/hplip:libnotify - Enables desktop notifications
net-print/hplip:minimal - Only build internal hpijs/hpcups driver (not recommended at all, make sure you know what you are doing)
net-print/hplip:parport - Enable parallel port for devices which require it
net-print/hplip:qt4 - Enable graphical interface using Qt 4
net-print/hplip:scanner - Enable scanner on multifunction devices which support it
net-print/hplip:snmp - Add support for net-analyzer/net-snmp which enables this driver to work over networks (both for server and client)
net-print/hplip:static-ppds - Use statically-generated PPDs instead of Dynamic PPDs. Although this is deprecated some printers may still need it to work properly. Use this flag if hp-setup fails to find/create a valid PPD file
net-print/hplip:udev-acl - Install udev acl rules which needs sys-fs/udev with acl support
net-print/pkpgcounter:psyco - psyco python accelerator
net-proxy/dansguardian:kaspersky - Adds support for Kaspersky AntiVirus software
net-proxy/dansguardian:ntlm - Enable support for the NTLM auth plugin
net-proxy/squid:ecap - Adds support for loadable content adaptation modules (http://www.e-cap.org)
net-proxy/squid:epoll - Enables Linux epoll() support
net-proxy/squid:icap-client - Adds ICAP client support
net-proxy/squid:ipf-transparent - Adds transparent proxy support for systems using IP-Filter (only for *bsd)
net-proxy/squid:kqueue - Enables *BSD kqueue() support
net-proxy/squid:logrotate - Use app-admin/logrotate for rotating logs
net-proxy/squid:pf-transparent - Adds transparent proxy support for systems using PF (only for *bsd)
net-proxy/squid:tproxy - Enables real Transparent Proxy support for Linux Netfilter TPROXY
net-proxy/squid:zero-penalty-hit - Add Zero Penalty Hit patch (http://zph.bratcheda.org)
net-proxy/sshproxy:client-only - Install only the client wrappers
net-proxy/tinyproxy:filter-proxy - Enable filtering of domains/URLS
net-proxy/tinyproxy:http-via-header - Add Via field to HTTP headers
net-proxy/tinyproxy:reverse-proxy - Enable reverse proxying
net-proxy/tinyproxy:transparent-proxy - Enable transparent proxying
net-proxy/tinyproxy:upstream-proxy - Enable upstream proxying
net-proxy/tinyproxy:xtinyproxy-header - Include the X-Tinyproxy header
net-proxy/tsocks:tordns -  Apply tordns patch which allows transparent TORification of the DNS queries 
net-proxy/ufdbguard:doc -  Download and install the ufdbguard reference manual in PDF. 
net-proxy/ufdbguard:httpd -  Build, install and start the provided mini-http daemon with the redirect CGI integrated. Since there is no way to tell ufdbguard to not start it, this is a build-time option. 
net-voip/ekiga:gconf - Enable GConf support
net-voip/ekiga:h323 - Enable H.323 protocol
net-voip/ekiga:shm - Enable the Shared Memory Extension from libXext
net-voip/ekiga:static - Statically link to opal and ptlib
net-voip/ekiga:xcap - Enable XML Configuration Access Protocal
net-voip/linphone:video - Enable video support (display/capture)
net-voip/sflphone:iax - Support for IAX (Inter Asterisk eXchange)
net-voip/telepathy-connection-managers:irc - Enable Internet Relay Chat (IRC) support.
net-voip/telepathy-connection-managers:jabber - Enable XMPP protocol handler (this is also Google Talk).
net-voip/telepathy-connection-managers:sip - Enable SIP/SIMPLE messaging and calling.
net-voip/telepathy-connection-managers:yahoo - Enable Yahoo! messaging support.
net-voip/telepathy-connection-managers:zeroconf - Enable Link-Local Messaging via the zeroconf or Bonjour protocol.
net-voip/yate:h323 - Build H.323 Channel plugin
net-voip/yate:ilbc - Build ILBC codec plugin
net-voip/yate:sctp -  Support for Stream Control Transmission Protocol 
net-voip/yate:spandsp - Enable support for the spandsp codec
net-voip/yate:zaptel - Build zaptel Channel plugin
net-wireless/blueman:network - Add functionality to setup (host) PAN connections using either net-dns/dnsmasq or net-misc/dhcp
net-wireless/bluez:attrib - Enable attrib plugin
net-wireless/bluez:consolekit - Use sys-auth/pambase[consolekit] to determine access to bluetooth devices based on whether a user is logged in locally or remotely
net-wireless/bluez:health - Compile with initial support for HDP
net-wireless/bluez:maemo6 - Compile with maemo6 plugin
net-wireless/bluez:old-daemons - Install old daemons like hidd and sdpd that are deprecated by the new Service framework
net-wireless/bluez:pnat - Enable pnat plugin
net-wireless/bluez:test-programs - Install tools for testing of various Bluetooth functions
net-wireless/gnome-bluetooth:introspection - Use dev-libs/gobject-introspection for introspection
net-wireless/gnome-bluetooth:nautilus - Build nautilus-sendto plugin
net-wireless/hostapd:debug - Enables debugging
net-wireless/hostapd:logwatch - Install support files for sys-app/logwatch
net-wireless/hostapd:madwifi - Add support for madwifi (Atheros chipset)
net-wireless/hostapd:wps - Add support for Wi-Fi Protected Setup
net-wireless/kismet:client - Build the ncurses-based user interface
net-wireless/kismet:pcap -  Enable packet capturing support using net-libs/libpcap 
net-wireless/kismet:suid -  Install a setuid root helper binary with limited functionality; this allows running kismet as a normal user, significantly reducing security risks 
net-wireless/madwifi-ng:injection - Adds support for net-wireless/aircrack-ng aireplay-ng packet injection
net-wireless/madwifi-old:amrr - Use Adaptive Multi Rate Retry bit rate control algorithm
net-wireless/madwifi-old:onoe - Use Atsushi Onoe's bit rate control algorithm
net-wireless/wepattack:john - Build with app-crypt/johntheripper support
net-wireless/wifiscanner:wireshark - Use the net-analyzer/wireshark wtap library
net-wireless/wireless-tools:multicall - Build the most commonly used tools as one binary
net-wireless/wpa_supplicant:eap-sim - Add support for EAP-SIM authentication algorithm
net-wireless/wpa_supplicant:fasteap - Add support for FAST-EAP authentication algorithm
net-wireless/wpa_supplicant:madwifi - Add support for madwifi (Atheros chipset)
net-wireless/wpa_supplicant:ps3 - Add support for ps3 hypervisor driven gelic wifi
net-wireless/wpa_supplicant:wimax - Add support for Wimax EAP-PEER authentication algorithm
net-wireless/wpa_supplicant:wps - Add support for Wi-Fi Protected Setup
rox-base/rox:video - Enable rox-extra/videothumbnail for creating thumbnails of videos with mplayer or totem.
rox-extra/archive:ace - Enable .ace extraction via app-arch/unace
rox-extra/archive:compress - Enable tar.Z and *.Z extraction via app-arch/ncompress
rox-extra/archive:cpio - Enable .cpio extraction via app-arch/cpio
rox-extra/archive:rar - Enable .rar extraction via app-arch/unrar
rox-extra/archive:rpm - Enable .rpm extraction via rpm2cpio from app-arch/rpm
rox-extra/archive:uuencode - Enable .uue extraction via app-arch/sharutils
rox-extra/archive:zip - Enable .zip extraction via app-arch/unzip and app-arch/zip
rox-extra/comicthumb:rar - Enable support for rar-compressed archives via app-arch/unrar
rox-extra/magickthumbnail:xcf - Enable previews of .xcf files using media-gfx/gimp
sci-astronomy/cpl:gasgano -  Enable support for sci-astronomy/gasgano file organizer 
sci-astronomy/orsa:cln - Use the Class Library for Numbers (sci-libs/cln) for calculations
sci-astronomy/predict:xforms - Add a "map" client which uses the x11-libs/xforms library for its GUI
sci-astronomy/predict:xplanet - Project predict data onto world maps generated by x11-misc/xplanet / x11-misc/xearth
sci-astronomy/scamp:plplot - Build with sci-libs/plplot to allow diagnostic plots during processing
sci-astronomy/stellarium:stars - Install extra star catalogs
sci-astronomy/wcslib:fits -  Enable support for the FITS format through sci-libs/cfitsio 
sci-astronomy/wcslib:pgplot -  Builds routines for the sci-libs/pgplot library 
sci-biology/bioperl:db - Install sci-biology/bioperl-run
sci-biology/bioperl:network - Install sci-biology/bioperl-run
sci-biology/bioperl:run - Install sci-biology/bioperl-run
sci-biology/clustalw-mpi:mpi_njtree - Use MPI (as opposed to serial) code for computing neighbor-joining trees
sci-biology/clustalw-mpi:static_pairalign - Use static (as opposed to dynamic) scheduling for pair alignments
sci-biology/exonerate:largefile - Enable largefile support on 32 bit systems
sci-biology/exonerate:utils - Install all utilities
sci-biology/fasta:icc - Use intel compiler instead of gcc
sci-biology/hmmer:pvm - Add support for parallel virtual machine (sys-cluster/pvm)
sci-biology/mcl:blast -  add support for NCBI BLAST data 
sci-biology/plink:R -  add support R language 
sci-biology/plink:webcheck -  add support for online update checking every time the program starts 
sci-biology/ucsc-genome-browser:server - Install genome browser Web application. If this flag is off, only libraries and utilities from the suite are installed.
sci-biology/yass:dmalloc - Enable debugging with the dmalloc library
sci-biology/yass:lowmem - Build for environments with low amounts of memory
sci-chemistry/PyMca:matplotlib - Support for plotting through matplotlib
sci-chemistry/apbs:arpack - Include support for arpack libs
sci-chemistry/apbs:fetk - Include support for FeTK
sci-chemistry/apbs:tools - Install optional tools
sci-chemistry/avogadro:glsl - Enable glsl features via GLEW.
sci-chemistry/caver:pymol - Install the PyMol plugin (sci-chemistry/pymol) 
sci-chemistry/ccp4:arpwarp - Add binary arp-warp for molecular replacement
sci-chemistry/ccp4:balbes - Install sci-chemistry/balbes
sci-chemistry/ccpn:extendnmr - Install needed packages for extendNMR support
sci-chemistry/cns:aria -  Support patch for sci-chemistry/aria
sci-chemistry/eden:double-precision - More precise calculations at the expense of speed
sci-chemistry/gamess:neo - Enable NEO for nuclear basis support
sci-chemistry/gamess:qmmm-tinker - Enable tinker qmmm code
sci-chemistry/ghemical:openbabel - Use sci-chemistry/openbabel for file conversions
sci-chemistry/ghemical:toolbar - Build the shortcuts toolbar
sci-chemistry/gromacs:dmalloc - Enable use of Debug Malloc
sci-chemistry/gromacs:double-precision - More precise calculations at the expense of speed
sci-chemistry/gromacs:ffamber - Enable ffamber ports for gromacs
sci-chemistry/gromacs:fkernels - Enable building of Fortran Kernels for platforms that dont have assembly loops
sci-chemistry/gromacs:single-precision - Single precision version of gromacs
sci-chemistry/gromacs:zsh-completion - Enable zsh completion support
sci-chemistry/gsim:emf - Support for .emf export
sci-chemistry/jmol:client-only - Install the viewer only, no applet files for httpd 
sci-chemistry/mopac7:gmxmopac7 - Add support library for gromacs
sci-chemistry/oasis:minimal - Restricts functionality on free software
sci-chemistry/openbabel:swig - Use swig to rebuild language bindings.
sci-chemistry/pdb2pqr:opal - Add web interface via opal
sci-chemistry/pdb2pqr:pdb2pka - Install experimental pdb2pka interface
sci-chemistry/pymol:apbs - Install the apbs plugin
sci-chemistry/pymol:numpy - Compile numpy support
sci-chemistry/pymol:shaders - Build with Shaders support - good for high-end 3D video cards.
sci-chemistry/pymol:vmd - Enable vmd module for trajectories
sci-chemistry/shelx:dosformat - Use CR/LF to end lines; useful in mixed Linux/Windows environments
sci-chemistry/vmd:msms - Add support for MSMS SAS calcualtion tool
sci-chemistry/vmd:povray - Add support for povray raytracer for HQ images
sci-chemistry/vmd:tachyon - Add support for tachyon raytracer for HQ images
sci-chemistry/wxmacmolplt:flash - Add support for flash movie generation using media-libs/ming
sci-electronics/geda:stroke - enable mouse gesture support
sci-electronics/gerbv:unit-mm - Set default unit for coordinates in status bar to mm
sci-electronics/gspiceui:schematics - Use sci-electronics/geda for schematics editing
sci-electronics/gspiceui:waveform - Use sci-electronics/gwave for waveform display
sci-electronics/gtkwave:fasttree - Enables experimental Fast SST Tree widget code.
sci-electronics/gtkwave:fatlines - Renders lines as double width in gtkwave.
sci-electronics/gtkwave:judy - Enables Judy array support.
sci-electronics/kicad:dev-doc - Install developer documentation (requires app-doc/doxygen)
sci-electronics/pcb:gcode - gcode file export
sci-electronics/pcb:gif - GIF graphics export
sci-electronics/pcb:jpeg - JPEG graphics export
sci-electronics/pcb:m4lib-png - Enable creating png previews for the m4 library
sci-electronics/pcb:nelma - NELMA file export
sci-electronics/pcb:png - PNG graphics export
sci-electronics/pcb:tk - Build tcl/tk graphical QFP footprint generator
sci-electronics/pcb:toporouter - Build toporouter
sci-electronics/pcb:xrender - Translucent PCB display for Motif/Lesstif GUI
sci-geosciences/gmt:gmtfull - Full resolution bathymetry database
sci-geosciences/gmt:gmthigh - Add high resolution bathymetry database
sci-geosciences/gmt:gmtsuppl - Supplement functions for GMT
sci-geosciences/gmt:gmttria - Non GNU triangulation method, more efficient
sci-geosciences/googleearth:mdns-bundled - Use bundled nss-mdns library instead of depending on sys-auth/nss-mdns. Enable this if you want to avoid the deptree.
sci-geosciences/googleearth:qt-bundled - Use bundled Qt4 libraries instead of system ones. Recommended only for troubleshooting.
sci-geosciences/gpsd:garmin - Enable support for Garmin simple text protocol
sci-geosciences/gpsd:gpsd_user - Add gpsd user for daemon privileges.
sci-geosciences/gpsd:minimal - Reduced install set, limited number of devices and client, no X deps
sci-geosciences/gpsd:ntp - Enable net-misc/ntp shared memory interface and PPS kernel support for GPS time
sci-geosciences/gpsd:ocean - Enable OceanServer support
sci-geosciences/gpsd:pl2303 - Enable udev rules for PL2303 USB-serial converter
sci-geosciences/gpsd:tntc - Enable True North Technologies digital compass support
sci-geosciences/grass:gmath - Enable gmath wrapper for BLAS/Lapack (virtual/blas, virtual/lapack)
sci-geosciences/grass:largefile - Enable LFS support for huge files
sci-geosciences/mapnik:gdal - Enable sci-libs/gdal library support
sci-geosciences/mapserver:agg - Enable x11-libs/agg library support
sci-geosciences/mapserver:flash - Add support for creating SWF files using media-libs/ming
sci-geosciences/mapserver:gdal - Enable sci-libs/gdal library support
sci-geosciences/mapserver:geos - Enable sci-libs/geos library support
sci-geosciences/mapserver:postgis - Enable dev-db/postgis support
sci-geosciences/mapserver:proj - Enable sci-libs/proj library support (geographic projections)
sci-geosciences/merkaartor:gdal - Enable sci-libs/gdal library support
sci-geosciences/merkaartor:proj - Enable sci-libs/proj library support
sci-geosciences/merkaartor:webkit - Enable net-libs/webkit-gtk library support
sci-geosciences/qgis:grass - Add support for sci-geosciences/grass
sci-libs/acml:gfortran - Fetch and install acml compiled with GNU gfortran
sci-libs/acml:ifc - Fetch and install acml compiled with Intel Fortran Compiler (dev-lang/ifc)
sci-libs/acml:int64 - Install the 64 bits integer library
sci-libs/arprec:qd - Use sci-libs/qd
sci-libs/blas-goto:int64 - Build the 64 bits integer library
sci-libs/cholmod:metis - Enable the Partition module to cholmod using metis (sci-libs/metis, sci-libs/parmetis)
sci-libs/cholmod:supernodal - Enable the Supernodal module (needs virtual/lapack)
sci-libs/fftw:float - Link default library to single precision instead of double (symlinks only and fftw-2.1)
sci-libs/gdal:aux_xml - Enable Portable Auxilliary Metadata generation
sci-libs/gdal:ecwj2k - Enable support for alternate jpeg2k library sci-libs/libecwj2
sci-libs/gdal:fits - Enable support for NASA's sci-libs/cfitsio library
sci-libs/gdal:geos - Add support for geometry engine (sci-libs/geos 
sci-libs/gdal:gml - Enable support for dev-libs/xerces-c C++ API
sci-libs/gdal:hdf - Add support for the Hierarchical Data Format v. 4 (sci-libs/hdf)
sci-libs/gdal:ogdi - Enable support for the open geographic datastore interface (sci-libs/ogdi)
sci-libs/gerris:dx - Enable support for sci-visualization/opendx
sci-libs/gsl:cblas-external - Link gsl with external cblas provided by (virtual/cblas) instead of shipped internal version
sci-libs/indilib:fits - Enable support for the FITS image format through cfitsio
sci-libs/indilib:nova - Enable support for nova celestial mechanics calculations
sci-libs/libcmatrix:atlas - Use of atlas blas implementation
sci-libs/libgeda:threads - Enable (posix) threads for the GTK GUI
sci-libs/libghemical:mopac7 - Use sci-chemistry/mopac7 for semi-empirical calculations
sci-libs/libghemical:mpqc - Use sci-chemistry/mpqc for quantum-mechanical calculations
sci-libs/libnc-dap:full-test - Enables full set of regression tests (long).
sci-libs/libsvm:tools - Install python based tool scripts
sci-libs/mathgl:octave - Add bindings for sci-mathematics/octave
sci-libs/metis:int64 - Build the 64 bits integer library (metis >=5 only)
sci-libs/mkl:fortran95 - Installs the BLAS/LAPACK FORTRAN95 static libraries
sci-libs/mkl:int64 - Installs the 64 bits integer libraries
sci-libs/mkl:serial - Installs the serial (as non-threaded) libraries
sci-libs/mpir:cpudetection - Enables runtime cpudetection (useful for bindist, compatability on other CPUs)
sci-libs/netcdf:dap - Support for remote data access with the built-in OPeNDAP client
sci-libs/nlopt:octave - Add plugin for sci-mathematics/octave
sci-libs/plplot:ada - Add bindings for the ADA programming language
sci-libs/plplot:d - Add bindings for the D programming language
sci-libs/plplot:dynamic - Build with dynamic drivers
sci-libs/plplot:octave - Add bindings for sci-mathematics/octave
sci-libs/plplot:qhull - Add bindings for media-libs/qhull bindings
sci-libs/scipy:umfpack - Adds support for sparse solving with sci-libs/umfpack
sci-libs/spqr:metis - Use METIS (sci-libs/metis or sci-libs/parmetis) for partitioning
sci-libs/spqr:tbb - Enable multithreading with the Intel Threads Building Block (needs dev-cpp/tbb)
sci-libs/suitesparse:metis -  Use METIS (sci-libs/metis or sci-libs/parmetis) for partitioning 
sci-libs/taucs:cilk - Enable multithreading using dev-lang/cilk)
sci-libs/umfpack:metis - Use METIS via CHOLMOD(sci-libs/cholmod) for partitioning
sci-libs/vtk:R - Enable support for dev-lang/R
sci-libs/vtk:boost - Add support for boost
sci-libs/vtk:cg - Use nvidia's cg shaders
sci-libs/vtk:patented - Build patented classes
sci-mathematics/Macaulay2:optimization - Accept upstream's choices for -O option, i.e. -O3 almost everywhere.
sci-mathematics/coq:norealanalysis - Do not build real analysis modules (faster compilation)
sci-mathematics/coq:realanalysis - Build real analysis modules (slower compilation)
sci-mathematics/dataplot:gs - Add Ghostscript support (app-text/ghostscript-gpl) 
sci-mathematics/freemat:arpack - Add sparse eigen value support via sci-libs/arpack
sci-mathematics/freemat:ffcall - Enable use of dev-libs/ffcall
sci-mathematics/freemat:umfpack - Add sparse solving via sci-libs/umfpack
sci-mathematics/freemat:volpack - Add volume rendering via media-libs/volpack
sci-mathematics/fricas:clisp - Add support for GNU CLISP (dev-lisp/clisp)
sci-mathematics/fricas:clozurecl - Add support for Clozure Common Lisp (dev-lisp/closurecl)
sci-mathematics/fricas:cmucl - Add support for CMU Common Lisp (dev-lisp/cmucl)
sci-mathematics/fricas:ecl - Add support for Embeddable Common Lisp (dev-lisp/ecls)
sci-mathematics/fricas:gcl - Add support for GNU Common Lisp (dev-lisp/gcl)
sci-mathematics/fricas:sbcl - Add support for Steel Bank Common Lisp (dev-lisp/sbcl)
sci-mathematics/geomview:avg - Enable experimental motion averaging technique
sci-mathematics/geomview:netpbm - Add media-libs/netpbm support for external modules
sci-mathematics/gretl:R - Enable support for dev-lang/R
sci-mathematics/gretl:sourceview - Enable support for x11-libs/gtksourceview 
sci-mathematics/maxima:clisp - Compile maxima with GNU CLISP (dev-lisp/clisp)
sci-mathematics/maxima:clozurecl - Compile maxima with Clozure Common Lisp (dev-lisp/clozurecl)
sci-mathematics/maxima:cmucl - Compile maxima with CMU Common Lisp (dev-lisp/cmucl)
sci-mathematics/maxima:ecl - Compile maxima with Embeddable Common Lisp (dev-lisp/ecls)
sci-mathematics/maxima:ecls - Compile maxima with Embeddable Common Lisp (dev-lisp/ecls)
sci-mathematics/maxima:gcl - Compile maxima with GNU Common Lisp (dev-lisp/gcl)
sci-mathematics/maxima:openmcl - Compile maxima with Clozure Common Lisp (former OpenMCL, dev-lisp/closurecl)
sci-mathematics/maxima:sbcl - Compile maxima with Steel Bank Common Lisp (dev-lisp/sbcl)
sci-mathematics/normaliz:extras -  Install sci-mathematics/Macaulay2 and sci-mathematics/singular packages as shipped by upstream
sci-mathematics/nusmv:minisat - Enable support for MiniSat
sci-mathematics/octave:sparse - Enable enhanced support for sparse matrix algebra
sci-mathematics/pari:data - Add additional data (elldata, galdata, seadata, nftables)
sci-mathematics/singular:boost - Compile against external boost headers (dev-libs/boost)
sci-mathematics/yacas:server - Build the network server version
sci-misc/boinc:client -  Build client part of the boinc. Not only the manager but also the computation unit. With +X only you will have only manager which can connect to remote clients. 
sci-misc/boinc:cuda -  Use nvidia cuda toolkit for speeding up computations. NOTE: works only for subset of nvidia graphic cards so make sure your card is supported before opening bug about it. 
sci-misc/brlcad:benchmarks -  Run benchmarks during test phase (need test option enabled) 
sci-misc/h5utils:octave - Build Octave plugins
sci-misc/nco:ncap2 - Build next generation netcdf arithmetic processor (needs dev-java/antlr)
sci-misc/nco:udunits - Add sci-libs/udunits files support
sci-misc/ncview:udunits - Add sci-libs/udunits files support
sci-physics/abinit:plugins - Build all plugins
sci-physics/bullet:extras - Build additional libraries
sci-physics/cernlib-montecarlo:herwig - Build Herwig internal event generator, newer version available in sci-physics/herwig
sci-physics/clhep:exceptions - Enable zoom exceptions for user intervention
sci-physics/geant:aida - Add support for Abstract Interfaces for Data Analysis 
sci-physics/geant:athena - Enable the MIT Athena (x11-libs/libXaw) widget set (default is Motif)
sci-physics/geant:data - Add a lot of standard physics data files for geant4
sci-physics/geant:dawn - Add support for media-gfx/dawn (3D postscript rendering)
sci-physics/geant:gdml - Enable geometry markup language for xml
sci-physics/geant:geant3 - Add compatibility for geant321 to geant4
sci-physics/geant:global - Produce a huge global library instead of small ones
sci-physics/geant:openinventor - Add support for media-libs/openinventor SGI toolkit
sci-physics/geant:raytracerx - Enable raytracing for physics events
sci-physics/geant:vrml - Enable output of geant4 in vrml formats
sci-physics/hepmc:cm - Build with cm instead of default mm for length units
sci-physics/hepmc:gev - Build with GeV instead of default MeV for momentum units
sci-physics/lhapdf:octave - Add bindings for sci-mathematics/octave
sci-physics/pythia:hepmc - Adds support for High Energy Physics Monte Carlo Generators sci-physics/hepmc
sci-physics/root:cint7 - Build the *experimental* new C++ interpretor CINT7
sci-physics/root:clarens -  Buld the Clarens and PEAC plug-ins, to use in a GRID enabled analysis.
sci-physics/root:geant4 - Build the sci-physics/geant (GEANT4) navigator
sci-physics/root:math - Build all math related libraries plugins, needs sci-libs/gsl 
sci-physics/root:pythia6 -  Builds the interface to Pythia-6 (sci-physics/pythia) high energy physics generation events library 
sci-physics/root:pythia8 -  Builds the interface to Pythia-8 (sci-physics/pythia) high energy physics generation events library 
sci-physics/root:reflex - Builds the reflection database for the C++ interpretor 
sci-physics/root:xrootd - Build the xrootd low latency file server
sci-visualization/gnuplot:gd - Add support for media-libs/gd. Needed for GIF, JPEG, and PNG image output.
sci-visualization/gnuplot:thin-splines - Enable thin plate splines
sci-visualization/gwyddion:sourceview -  Enable support for x11-libs/gtksourceview 
sci-visualization/hippodraw:fits -  Enable HippoDraw's built-in support for reading FITS files, by using the CFITSIO library. FITS binary and ASCII tables are supported as well as images. When combine with numpy flag, it can also use the pyfits package. 
sci-visualization/hippodraw:numpy -  Enable support for the numerical array manipulation and computational capabilities of numpy in python. HippoDraw can return a numerical array to Python from any of the type of objects that are supported. One can also import data to a HippoDraw from a numpy array. 
sci-visualization/hippodraw:root -  Adds support for ROOT input/ouput system, storing a table of data as TBranch objects each with a single TLeaf. Files of this type can be imported by HippoDraw as a RootNTuple. Also if root flag is selected, it can use root::minuit for minimization instead of standalone minuit library. 
sci-visualization/hippodraw:wcs -  Adds 10 built-in transforms to HippoDraw via the World Coordinate System library for FITS files. 
sci-visualization/opendx:cdf - Add support for sci-libs/cdf data exchange format
sci-visualization/opendx:hdf - Add support for the Hierarchical Data Format (sci-libs/hdf)
sci-visualization/paraview:boost - Enable the usage of dev-libs/boost
sci-visualization/paraview:cg - Add support for nvidia's cg shaders
sci-visualization/paraview:gui - Build paraview's gui not just the server
sci-visualization/paraview:overview - Enable the OverView plugin framework
sci-visualization/paraview:plugins - Build and install additional plugins
sci-visualization/paraview:streaming - Enable streaming paraview application
sci-visualization/qtiplot:emf - Export support for Windows Enhanced Metafile
sci-visualization/qtiplot:ods - Import support for OpenOffice .ods sheets
sci-visualization/qtiplot:origin - Import support for Origin project files
sci-visualization/qtiplot:xls - Import support for Microsoft office excel sheets
sci-visualization/veusz:fits - Add FITS format via dev-python/pyfits
sec-policy/selinux-base-policy:open_perms - Enable the open permissions for file object classes (SELinux policy capability).
sec-policy/selinux-base-policy:peer_perms - Enable the labeled networking peer permissions (SELinux policy capability).
sys-apps/acl:nfs -  add support for NFS acls 
sys-apps/busybox:make-symlinks - Create all the appropriate symlinks in /bin and /sbin.
sys-apps/busybox:mdev - Create the appropriate symlink in /sbin and install mdev.conf and support files
sys-apps/flashrom:atahpt - Highpoint (HPT) ATA/RAID controller support
sys-apps/flashrom:bitbang_spi - Bitbanging SPI infrastructure
sys-apps/flashrom:buspirate_spi - Enable Bus Pirate SPI programmer
sys-apps/flashrom:buspiratespi - Enable Bus Pirate SPI programmer
sys-apps/flashrom:dediprog - Dediprog SF100 support
sys-apps/flashrom:drkaiser - Enable Dr. Kaiser programmer
sys-apps/flashrom:dummy - Enable dummy tracing
sys-apps/flashrom:ft2232_spi - Enable ftdi programmer, flashing through FTDI/SPI USB interface
sys-apps/flashrom:ftdi - Enable ftdi programmer, flashing through FTDI/SPI USB interface
sys-apps/flashrom:gfxnvidia - Enable NVIDIA programmer
sys-apps/flashrom:internal - Enable internal/onboard support
sys-apps/flashrom:nic3com - Enable 3Com NIC programmer
sys-apps/flashrom:nicintel_spi - Support for SPI on Intel NICs
sys-apps/flashrom:nicnatsemi - Support for National Semiconductor NICs
sys-apps/flashrom:nicrealtek - Support for Realtek NICs
sys-apps/flashrom:nvidia - Enable NVIDIA programmer
sys-apps/flashrom:rayer_spi - RayeR SPIPGM hardware support
sys-apps/flashrom:satasii - Enable programmer for SiI SATA controllers
sys-apps/flashrom:serprog - Enable Serial Flasher programmer
sys-apps/flashrom:wiki - Enable wiki informations, like supported devices etc.
sys-apps/gnome-disk-utility:fat - Include FAT16/FAT32 support (sys-fs/dosfstools)
sys-apps/gnome-disk-utility:nautilus - Enable gnome-base/nautilus extension.
sys-apps/gnome-disk-utility:remote-access - Enable access to remote udisks daemons.
sys-apps/hal:acpi - Enables HAL to attempt to read from /proc/acpi/event, if unavailable, HAL will read events from sys-power/acpid. If you need multiple acpi readers, ensure acpid is in your default runlevel (rc-update add acpid default) along with HAL. This will also enable HAL to read Toshiba and IBM acpi events which do not get sent via /proc/acpi/event
sys-apps/hal:consolekit - Enables HAL to interact with consolekit for determining whether a given process is running on behalf of the person setting at the console.
sys-apps/hal:crypt - Allows HAL to mount volumes that are encrypted using LUKS. sys-fs/cryptsetup-luks which has recently been renamed to sys-fs/cryptsetup allows you to create such encrypted volumes. HAL will be able to handle volumes that are removable or fixed.
sys-apps/hal:dell - Builds and installs the Dell addon, which reads data from the Dell SM BIOS via sys-libs/libsmbios. It will read your service tag information and your hardware backlight data as well as allow you to modify the backlight settings on a Dell laptop.
sys-apps/hal:disk-partition - Allows HAL to use libparted from sys-block/parted to read raw partition data from your disks and process that data. Future versions of HAL (possibly 0.5.11 and higher) will allow you to create, modify, delete and format partitions from a GUI interface agnostic of your desktop environment.
sys-apps/hal:doc - Generates documentation that describes HAL's fdi format.
sys-apps/hal:laptop - Adds support for power management scripts (sys-power/pm-utils)
sys-apps/hal:selinux - Installs SELinux policies and links HAL to the SELinux libraries.
sys-apps/halevt:rpath - Hardcode runtime library paths
sys-apps/hwdata-gentoo:binary-drivers - Adds support for ATI/NVIDIA binary drivers
sys-apps/ipmitool:openipmi - Use the system OpenIPMI implementation.
sys-apps/iproute2:iptables - include support for iptables filtering
sys-apps/kexec-tools:lzma - Enables support for LZMA compressed kernel images
sys-apps/kexec-tools:xen - Enable extended xen support
sys-apps/lm_sensors:sensord - Enable sensord - a daemon that can be used to periodically log sensor readings from hardware health-monitoring chips
sys-apps/man:lzma - Uses app-arch/lzma-utils for the COMPRESS feature. Could also be used to guarantee that lzma is on the system.
sys-apps/memtest86:serial - Compile with serial console support
sys-apps/memtest86+:floppy - Install a script to create floppy disks containing memtest86+ binaries.
sys-apps/memtest86+:serial - Compile with serial console support
sys-apps/paludis:inquisitio - Enable inquisitio, the search client
sys-apps/paludis:pbins - Enable binary package support. Adds dependency upon app-arch/libarchive
sys-apps/paludis:pink - Use a less boring colourscheme than the default
sys-apps/paludis:portage - Enable experimental support for Portage configuration formats
sys-apps/paludis:python-bindings - Enable Python bindings. Requires a lot of RAM to build (~700Mbytes per job) and adds a dependency upon dev-libs/boost
sys-apps/paludis:ruby-bindings - Enable Ruby bindings.
sys-apps/paludis:search-index - Enable cave search --index. Requires sqlite.
sys-apps/paludis:visibility - Enable visibility support (g++ >=4.1)
sys-apps/pciutils:network-cron -  Monthly cronjob the update-pciids script 
sys-apps/pcmcia-cs:trusted - Assume all users are trusted (Build unsafe user-space tools)
sys-apps/pcmcia-cs:xforms - Enable building the xforms based cardinfo binary
sys-apps/pcmcia-cs-modules:cardbus - Enable 32bit CardBus support
sys-apps/pcmciautils:staticsocket - Add support for static sockets
sys-apps/portage:epydoc - Build html API documentation with epydoc.
sys-apps/portage:ipc - Use inter-process communication between portage and running ebuilds.
sys-apps/portage:python3 - Use python3 as Python interpreter.
sys-apps/pyrenamer:music - Enable support for renaming music
sys-apps/qingy:opensslcrypt - Encrypt communications between qingy and its GUI using dev-libs/openssl
sys-apps/s390-tools:fuse - build cmsfs-fuse to read files stored on a z/VM CMS disk
sys-apps/s390-tools:zfcpdump - build the kernel disk dumping utility
sys-apps/shadow:audit - Enable support for sys-process/audit
sys-apps/shadow:nousuid - When nousuid is enabled only su from the shadow package will be installed with the setuid bit (mainly for single user systems)
sys-apps/smartmontools:minimal - Do not install the monitoring daemon and associated scripts.
sys-apps/tuxonice-userui:fbsplash - Add support for framebuffer splash
sys-apps/ucspi-ssl:tls - Add TLS support (see also http://www.suspectclass.com/~sgifford/ucspi-tls/)
sys-apps/usbutils:network-cron - Monthly cronjob the update-usbids script
sys-apps/usermode-utilities:fuse - Build tools (currently umlmount) needing fuse
sys-apps/util-linux:cramfs - build mkfs/fsck helpers for cramfs filesystems
sys-apps/util-linux:loop-aes - include support for Loop AES encryption
sys-apps/util-linux:perl - install the chkdupexe helper script
sys-apps/v86d:x86emu - Use x86emu for Video BIOS calls
sys-auth/consolekit:policykit -  Use the PolicyKit framework (sys-auth/polkit) to get authorization for suspend/shutdown. 
sys-auth/munge:gcrypt - Use libgcrypt instead of openssl
sys-auth/pam_mysql:openssl - Use OpenSSL for md5 and sha1 support
sys-auth/pam_pkcs11:nss -  Use Mozilla NSS (dev-libs/nss) as provider for PKCS#11 access, rather than using OpenSSL with a custom implementation of the PKC#11 protocol. 
sys-auth/pam_pkcs11:pcsc-lite -  Build the card_eventmanager binary used to detect card removal and lock the sessions. This needs sys-apps/pcsc-lite. 
sys-auth/pambase:consolekit -  Enable pam_ck_connector module on local system logins. This allows for console logins to make use of ConsoleKit authorization. 
sys-auth/pambase:cracklib -  Enable pam_cracklib module on system authentication stack. This produces warnings when changing password to something easily crackable. It requires the same USE flag to be enabled on sys-libs/pam or system login might be impossible. 
sys-auth/pambase:debug -  Enable debug information logging on syslog(3) for all the modules supporting this in the system authentication and system login stacks. 
sys-auth/pambase:gnome-keyring -  Enable pam_gnome_keyring module on system login stack. This enables proper Gnome Keyring access to logins, whether they are done with the login shell, a Desktop Manager or a remote login systems such as SSH. 
sys-auth/pambase:minimal -  Disables the standard PAM modules that provide extra information to users on login; this includes pam_tally (and pam_tally2 for Linux PAM 1.1 and later), pam_lastlog, pam_motd and other similar modules. This might not be a good idea on a multi-user system but could reduce slightly the overhead on single-user non-networked systems. 
sys-auth/pambase:mktemp -  Enable pam_mktemp module on system auth stack for session handling. This module creates a private temporary directory for the user, and sets TMP and TMPDIR accordingly. 
sys-auth/pambase:pam_krb5 -  Enable pam_krb5 module on system auth stack, as an alternative to pam_unix. If Kerberos authentication succeed, only pam_unix will be ignore, and all the other modules will proceed as usual, including Gnome Keyring and other session modules. It requires sys-libs/pam as PAM implementation. 
sys-auth/pambase:pam_ssh -  Enable pam_ssh module on system auth stack for authentication and session handling. This module will accept as password the passphrase of a private SSH key (one of ~/.ssh/id_rsa, ~/.ssh/id_dsa or ~/.ssh/identity), and will spawn an ssh-agent instance to cache the open key. 
sys-auth/pambase:passwdqc -  Enable pam_passwdqc module on system auth stack for password quality validation. This is an alternative to pam_cracklib producing warnings, rejecting or providing example passwords when changing your system password. It is used by default by OpenWall GNU/*/Linux and by FreeBSD. 
sys-auth/pambase:sha512 -  Switch Linux-PAM's pam_unix module to use sha512 for passwords hashes rather than MD5. This option requires >=sys-libs/pam-1.0.1 built against >=sys-libs/glibc-2.7, if it's built against an earlier version, it will silently be ignored, and MD5 hashes will be used. All the passwords changed after this USE flag is enabled will be saved to the shadow file hashed using SHA512 function. The password previously saved will be left untouched. Please note that while SHA512-hashed passwords will still be recognised if the USE flag is removed, the shadow file will not be compatible with systems using an earlier glibc version. 
sys-auth/polkit:introspection - Use dev-libs/gobject-introspection for introspection
sys-block/gparted:btrfs - Include Btrfs support (sys-fs/btrfs-progs)
sys-block/gparted:dmraid - Support for dmraid devices, also known as ATA-RAID, or Fake RAID.
sys-block/gparted:fat - Include FAT16/FAT32 support (sys-fs/dosfstools) 
sys-block/gparted:hfs - Include HFS support (sys-fs/hfsutils)
sys-block/gparted:jfs - Include JFS support (sys-fs/jfsutils)
sys-block/gparted:mdadm - Support for Linux software RAID.
sys-block/gparted:ntfs - Include NTFS support (sys-fs/ntfsprogs)
sys-block/gparted:reiser4 - Include ReiserFS4 support (sys-fs/reiser4progs)
sys-block/gparted:reiserfs - Include ReiserFS support (sys-fs/reiserfsprogs)
sys-block/gparted:xfce - Enable integration in XFCE desktop
sys-block/gparted:xfs - Include XFS support (sys-fs/xfsprogs, sys-fs/xfsdump)
sys-block/open-iscsi:modules - Build the open-iscsi kernel modules
sys-block/open-iscsi:utils - Build the open-iscsi utilities
sys-block/parted:debug -  Enable debugging as encouraged by upstream: [The default configuration] includes --enable-debug (by default), which contains many assertions. Obviously, these "waste" space, but in the past, they have caught potentially dangerous bugs before they would have done damage, so we think it's worth it. Also, it means we get more bug reports ;) 
sys-block/parted:device-mapper -  Enable sys-fs/device-mapper support in parted 
sys-block/partimage:nologin - Do not include login support when connecting partimaged
sys-block/tgt:fcoe - Add support for FCoE protocol
sys-block/tgt:fcp - Add support for new FC protocol
sys-block/tgt:ibmvio - Add support for IBM Virtual I/O
sys-block/tgt:infiniband - Add support for iSCSI over RDMA (iser). All needed libs can be found in science overlay
sys-block/unieject:pmount - Make use of pmount wrapper and pmount-like permissions (sys-apps/pmount)
sys-boot/arcboot:cobalt - Disable support for Cobalt Microserver hardware (Qube2/RaQ2)
sys-boot/arcboot:ip27 - Disable support for SGI Origin (IP27)
sys-boot/arcboot:ip28 - Disable support for SGI Indigo2 Impact R10000 (IP28)
sys-boot/arcboot:ip30 - Disable support for SGI Octane (IP30)
sys-boot/grub:multislot - Allow grub1 and grub2 to be installed simultaneously
sys-boot/lilo:device-mapper - Enable support for sys-fs/device-mapper
sys-boot/lilo:pxeserial - Avoid character echo on PXE serial console
sys-cluster/ceph:fuse - Build fuse client
sys-cluster/ceph:libatomic - Use libatomic instead of builtin atomic operations
sys-cluster/ceph:radosgw - Add radosgw support
sys-cluster/charm:cmkopt - Enable CMK optimisation
sys-cluster/charm:tcp - Use TCP (instead of UPD) for socket communication
sys-cluster/corosync:infiniband - Enable Infiniband RDMA transport support
sys-cluster/drbd:heartbeat - Enable Heartbeat integration
sys-cluster/drbd:pacemaker - Enable Pacemaker integration
sys-cluster/drbd:xen - Enable Xen integration
sys-cluster/gearmand:drizzle -  Support dev-db/libdrizzle for the queue storage. This also adds support for MySQL storage. 
sys-cluster/gearmand:memcache -  Support memcache daemon (via dev-libs/libmemcached) for the queue storage. 
sys-cluster/gearmand:tcmalloc -  Use the dev-util/google-perftools libraries to replace the malloc() implementation with a possibly faster one. 
sys-cluster/gearmand:tokyocabinet -  Support dev-db/tokyocabinet for the queue storage. 
sys-cluster/glusterfs:extras - Install extra helper scripts
sys-cluster/glusterfs:fuse - Add FUSE mount helper
sys-cluster/glusterfs:infiniband - Add support for Infiniband ibverbs transport. Libraries can be found in science overlay
sys-cluster/heartbeat:ipmi - Enable IPMILan Stonith Plugin
sys-cluster/heartbeat:ldirectord - Adds support for ldiretord, use enabled because it has a lot of deps
sys-cluster/heartbeat:management - Adds support for management GUI
sys-cluster/lam-mpi:pbs - Add support for the Portable Batch System (PBS)
sys-cluster/lam-mpi:romio - Enable romio, a high-performance portable MPI-IO implementation
sys-cluster/lam-mpi:xmpi - Build support for the external XMPI debugging GUI
sys-cluster/mpi-dotnet:doc - Install tutorials for C# and IronPython (requires a Word document reader)
sys-cluster/mpi-dotnet:examples - Install small, illustrative projects using MPI.Net
sys-cluster/mpich2:mpi-threads - Enable MPI_THREAD_MULTIPLE
sys-cluster/mpich2:romio - Enable romio, a high-performance portable MPI-IO implementation
sys-cluster/ocfs:aio - Add aio support
sys-cluster/openmpi:heterogeneous - Enable features required for heterogeneous platform support
sys-cluster/openmpi:mpi-threads - Enable MPI_THREAD_MULTIPLE
sys-cluster/openmpi:pbs - Add support for the Portable Batch System (PBS)
sys-cluster/openmpi:romio - Build the ROMIO MPI-IO component
sys-cluster/openmpi:vt - Enable bundled VampirTrace support
sys-cluster/pacemaker:ais - Enable sys-cluster/openais support.
sys-cluster/pacemaker:heartbeat - Enable sys-cluster/heartbeat support.
sys-cluster/pacemaker:smtp - Enable SMTP support via net-libs/libsmtp
sys-cluster/pvfs2:apidocs - Build API documentation directly from the code using doxygen
sys-cluster/pvfs2:server - Enable compilation of server code
sys-cluster/torque:cpusets - Enable pbs_mom to utilize linux cpusets if available.
sys-cluster/torque:drmaa - Enable the Distributed Resource Management Application API.
sys-cluster/torque:server - Enable compilation of pbs_server and pbs_sched.
sys-devel/binutils:multislot - Allow for multiple versions of binutils to be emerged at once for same CTARGET
sys-devel/binutils:multitarget - Adds support to binutils for cross compiling (does not work with gas)
sys-devel/binutils-apple:lto - Add support for Link-Time Optimization with LLVM
sys-devel/binutils-hppa64:multislot - Allow for multiple versions of binutils to be emerged at once for same CTARGET
sys-devel/binutils-hppa64:multitarget - Adds support to binutils for cross compiling (does not work with gas)
sys-devel/clang:alltargets - Build all host targets (default: host only)
sys-devel/clang:static-analyzer - Install the Clang static analyzer
sys-devel/clang:system-cxx-headers - By default, clang++ searchs for C++ headers in a series of hardcoded paths. Enabling this flag will force it to use the active gcc profile ones
sys-devel/gcc:d - Enable support for the D programming language
sys-devel/gcc:fixed-point - Enable fixed-point arithmetic support for MIPS targets in gcc (Warning: significantly increases compile time!)
sys-devel/gcc:graphite - Add support for the framework for loop optimizations based on a polyhedral intermediate representation
sys-devel/gcc:ip28 - Enable building a compiler capable of building a kernel for SGI Indigo2 Impact R10000 (IP28)
sys-devel/gcc:ip32r10k - Enable building a compiler capable of building an experimental kernel for SGI O2 w/ R1x000 CPUs (IP32)
sys-devel/gcc:libffi - Build the portable foreign function interface library
sys-devel/gcc:lto - Add support for link-time optimizations (unsupported, use at your own risk).
sys-devel/gcc:mudflap - Add support for mudflap, a pointer use checking library
sys-devel/gcc:multislot - Allow for SLOTs to include minor version (3.3.4 instead of just 3.3)
sys-devel/gcc:n32 - Enable n32 ABI support on mips
sys-devel/gcc:n64 - Enable n64 ABI support on mips
sys-devel/gcc:nopie - Disable PIE support (NOT FOR GENERAL USE)
sys-devel/gcc:nossp - Disable SSP support (NOT FOR GENERAL USE)
sys-devel/gcc:objc - Build support for the Objective C code language
sys-devel/gcc:objc++ - Build support for the Objective C++ language
sys-devel/gcc:objc-gc - Build support for the Objective C code language Garbage Collector
sys-devel/gcc-apple:multislot - Allow for SLOTs to include minor version (3.3.4 instead of just 3.3)
sys-devel/gcc-apple:objc - Build support for the Objective C code language
sys-devel/gcc-apple:objc++ - Build support for the Objective C++ language
sys-devel/gdb:multitarget - Support all known targets in one gdb binary
sys-devel/gettext:git - When running `autopoint`, use git to store the internal development files; this requires git at runtime, but will be faster/smaller than raw archives
sys-devel/kgcc64:multislot - Allow for SLOTs to include minor version (eg. 3.3.4 instead of just 3.3)
sys-devel/libperl:ithreads - Enable Perl threads, has some compatibility problems
sys-devel/llvm:alltargets - Build all host targets (default: host only)
sys-devel/llvm:libffi - Add support to call arbitrary external (natively compiled) functions via dev-libs/libffi
sys-devel/llvm:llvm-gcc - Build LLVM with sys-devel/llvm-gcc
sys-devel/llvm:udis86 - Enable support for dev-libs/udis86 disassembler library
sys-devel/llvm-gcc:bootstrap - Compile the final llvm-gcc executables with llvm-gcc itself
sys-devel/llvm-gcc:objc - Build support for the Objective C code language
sys-devel/llvm-gcc:objc++ - Build support for the Objective C++ language
sys-freebsd/boot0:tftp - Enable PXE/TFTP boot support.
sys-freebsd/boot0:zfs - Enable booting on ZFS filesystems.
sys-freebsd/freebsd-lib:hesiod - Enable support for net-dns/hesiod
sys-freebsd/freebsd-lib:netware -  Build libraries and tools to work with NetWare protocols (IPX and NCP). 
sys-freebsd/freebsd-rescue:zfs - Enable ZFS support.
sys-freebsd/freebsd-sbin:ipfilter -  Build tools to administer the ipfilter firewall. 
sys-freebsd/freebsd-sbin:netware -  Build libraries and tools to work with NetWare protocols (IPX and NCP). 
sys-freebsd/freebsd-sbin:pf -  Build tools to administer the PF firewall. 
sys-freebsd/freebsd-share:isdn - Enable ISDN support
sys-freebsd/freebsd-ubin:ar -  Build FreeBSD's ar and ranlib replacements based on libarchive. The toolchain will still use binutils' version but you can play with it. They have been renamed to freebsd-ar and freebsd-ranlib not to collide with binutils. 
sys-freebsd/freebsd-ubin:audit -  Build auditing tools. 
sys-freebsd/freebsd-ubin:netware -  Build libraries and tools to work with NetWare protocols (IPX and NCP). 
sys-freebsd/freebsd-ubin:zfs - Enable ZFS support (for fstat actually).
sys-freebsd/freebsd-usbin:audit -  Build auditing tools. 
sys-freebsd/freebsd-usbin:floppy - Enable floppy disk utilities (fdcontrol, fdformat, fdread, fdwrite).
sys-freebsd/freebsd-usbin:isdn - Enable ISDN support.
sys-freebsd/freebsd-usbin:netware -  Build libraries and tools to work with NetWare protocols (IPX and NCP). 
sys-fs/aufs2:debug - Enable additional debugging support
sys-fs/aufs2:inotify - Enable inotify support
sys-fs/aufs2:kernel-patch - Patch the current kernel for aufs2 support
sys-fs/aufs2:nfs - Enable support for nfs export
sys-fs/aufs2:ramfs - Enable initramfs/rootfs support
sys-fs/btrfs-progs:debug-utils - Build additional utils for debugging
sys-fs/cryptsetup:dynamic - Build cryptsetup dynamically
sys-fs/dmraid:dietlibc - Compile against dev-libs/dietlibc
sys-fs/dmraid:intel_led - Enable Intel LED support
sys-fs/dmraid:klibc - Compile against dev-libs/klibc
sys-fs/dmraid:led - Enable LED support
sys-fs/dmraid:mini - Create a minimal binary suitable for early boot environments
sys-fs/ecryptfs-utils:gpg - Enable app-crypt/gnupg key module
sys-fs/ecryptfs-utils:openssl - Enable dev-libs/openssl key module
sys-fs/ecryptfs-utils:pkcs11 - Enable PKCS#11 (Smartcards) key module
sys-fs/ecryptfs-utils:tpm - Enable support for Trusted Platform Module (TPM) using app-crypt/trousers
sys-fs/evms:hb - Enable support for heartbeat-1
sys-fs/evms:hb2 - Enable support for heartbeat-2
sys-fs/loop-aes:extra-ciphers - Enable extra ciphers
sys-fs/loop-aes:keyscrub - Protects the encryption key in memory but takes more cpu resources
sys-fs/loop-aes:padlock - Use VIA padlock instructions, detected at run time, code still works on non-padlock processors
sys-fs/lvm2:clvm - Allow users to build clustered lvm2
sys-fs/lvm2:cman - Cman support for clustered lvm
sys-fs/lvm2:lvm1 - Allow users to build lvm2 with lvm1 support
sys-fs/lvm2:nolvmstatic - Allow users to build lvm2 dynamically
sys-fs/ntfs3g:external-fuse - Use external FUSE library instead of internal one. Must be disabled for unprivileged mounting to work.
sys-fs/ntfs3g:udev - Install udev rule to make udisks use ntfs-3g instead of the kernel NTFS driver.
sys-fs/ntfsprogs:fuse - Build a FUSE module
sys-fs/owfs:ftpd - Enable building the OWFS FTP server (owftpd)
sys-fs/owfs:fuse - Enable building the FUSE-based OWFS client (owfs)
sys-fs/owfs:httpd - Enable building the OWFS web server (owhttpd)
sys-fs/owfs:parport - Enable support for the DS1410E parallel port adapter
sys-fs/owfs:server - Enable building the OWFS server (owserver)
sys-fs/pysize:psyco - Adds psyco support
sys-fs/quota:rpc - Enable quota interaction via RPC
sys-fs/udev:devfs-compat - Install rules for devfs compatible device names
sys-fs/udev:extras - Compile udev-extras requiring external dependencies
sys-fs/udev:old-hd-rules - Install rules for /dev/hd* devices, removed upstream at udev-148
sys-fs/udisks:remote-access - Control whether connections from other clients over LAN are allowed
sys-fs/unionfs:nfs - Adds support for NFS file system
sys-kernel/ck-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/dracut:bootchart - Add support for bootchart (app-benchmarks/bootchart)
sys-kernel/dracut:btrfs - Add support for root on Btrfs
sys-kernel/dracut:crypt - Add support for encrypted partitions with cryptsetup/LUKS
sys-kernel/dracut:debug - Module installing additional tools like strace, file editor, ssh and more
sys-kernel/dracut:dmraid - Add support for dmraid devices, also known as ATA-RAID, or Fake RAID.
sys-kernel/dracut:dmsquash-live - Module which might be used for Live CDs
sys-kernel/dracut:gensplash - Add support for framebuffer splash at boot-time
sys-kernel/dracut:iscsi - Add support for iSCSI
sys-kernel/dracut:lvm - Add support for the Logical Volume Manager (sys-apps/lvm2)
sys-kernel/dracut:md - Add support for MD devices, also known as software RAID devices
sys-kernel/dracut:mdraid - Add support for MD devices, also known as software RAID devices
sys-kernel/dracut:multipath - Add support for Device Mapper multipathing
sys-kernel/dracut:nbd - Add support for network block devices
sys-kernel/dracut:nfs - Add support for NFS
sys-kernel/dracut:uswsusp - Add support for uswsusp (sys-power/suspend)
sys-kernel/dracut:xen - Add support for Xen
sys-kernel/gentoo-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/gentoo-sources:ultra1 - Enable if you have a SUN Ultra 1 with a HME interface
sys-kernel/hardened-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/linux-docs:html - Install HTML documentation
sys-kernel/mips-sources:cobalt - Enables support for Cobalt Microserver hardware (Qube2/RaQ2)
sys-kernel/mips-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/mips-sources:impactdebug - Enables use of the Impact Early Console Hack. FOR DEBUGGING ONLY!
sys-kernel/mips-sources:ip27 - Enables support for SGI Origin (IP27)
sys-kernel/mips-sources:ip28 - Enables support for SGI Indigo2 Impact R10000 (IP28)
sys-kernel/mips-sources:ip30 - Enables support for SGI Octane (IP30, 'Speedracer')
sys-kernel/mips-sources:ip32r10k - Enables experimental support for IP32 R10K kernels (SGI O2, 'Moosehead')
sys-kernel/mm-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/openvz-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/pf-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/pf-sources:experimental - Apply patches that are considered experimental. For more information, check out the ChangeLog or the ebuild that interests you.
sys-kernel/sparc-sources:ultra1 - If you have a SUN Ultra 1 with a HME interface
sys-kernel/tuxonice-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/vanilla-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/vserver-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/xen-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/zen-sources:bfq - Make the BFQ IO Scheduler available by applying upstream patches
sys-kernel/zen-sources:deblob - Remove binary blobs from kernel sources to provide libre license compliance.
sys-kernel/zen-sources:stable - Clone stable git tree
sys-libs/glibc:glibc-compat20 - Enable the glibc-compat addon
sys-libs/glibc:glibc-omitfp - Configure glibc with --enable-omitfp which lets the build system determine when it is safe to use -fomit-frame-pointer
sys-libs/glibc:nptlonly - Disables building the linuxthreads fallback in glibc ebuilds that support building both linuxthread and nptl
sys-libs/gwenhywfar:fox - Use x11-libs/fox graphical toolkit
sys-libs/libraw1394:juju - Use the new juju firewire stack in the Linux kernel
sys-libs/ncurses:ada - Add bindings for the ADA programming language
sys-libs/ncurses:trace - Enable test trace() support in ncurses calls
sys-libs/pam:audit - Enable support for sys-process/audit
sys-libs/pam:berkdb -  Build the pam_userdb module, that allows to authenticate users against a Berkeley DB file. Please note that enabling this USE flag will create a PAM module that links to the Berkeley DB (as provided by sys-libs/db) installed in /usr/lib and will thus not work for boot-critical services authentication. 
sys-libs/pam:cracklib -  Build the pam_cracklib module, that allows to verify the chosen passwords' strength through the use of sys-libs/cracklib. Please note that simply enabling the USE flag on this package will not make use of pam_cracklib by default, you should also enable it in sys-auth/pambase as well as update your configuration files. 
sys-libs/talloc:compat - Enable extra compatibility stuff
sys-libs/talloc:swig - Install interface definitions for dev-lang/swig
sys-libs/tdb:tdbtest - Install tdbtest app
sys-libs/tdb:tools - Install extra tools
sys-libs/uclibc:pregen - Use pregenerated locales
sys-libs/uclibc:savedconfig - Adds support for user defined configs
sys-libs/uclibc:ssp - Force the use of ssp to be built into a hardened uclibc setup
sys-libs/uclibc:uclibc-compat - Build uclibc with backwards compatible options
sys-libs/uclibc:userlocales - Build only the locales specified in /etc/locales.build
sys-libs/uclibc:wordexp - Add support for word expansion (wordexp.h)
sys-power/cpufreqd:nforce2 - Enable support for nforce2 voltage settings plug-in
sys-power/cpufreqd:nvidia - Enable nvidia overclocking (media-video/nvclock) plug-in
sys-power/cpufreqd:pmu - Enable Power Management Unit plug-in
sys-power/nvclock:gtk - Install the GTK+ based graphical interface
sys-power/phctool:sudo - Enable support for sudo to run gui from non-root user
sys-power/pm-utils:ntp - Install support for net-misc/ntp
sys-power/powerman:genders -  Add support for selecting power control targets using genders (-g option) 
sys-power/powerman:httppower -  Add support for HTTP based power controllers 
sys-power/powermgmt-base:pm-utils - Adds support for on_ac_power through sys-power/pm-utils
sys-power/suspend:crypt - Allows suspend and resume from encrypted disk
sys-power/suspend:fbsplash - Add support for framebuffer splash
sys-power/upower:introspection - Use dev-libs/gobject-introspection for introspection
sys-process/cronie:inotify - Enable inotify filesystem monitoring support.
sys-process/fcron:debug -  Enable debug code and output. Since version 3.0.5 this will no longer force foreground execution, and fcron will be able to run as a service properly. 
sys-process/fcron:pam -  Enable PAM support for fcron. This means that fcron will pass through the "fcron" stack before executing the jobs, and fcrontab will use the "fcrontab" stack to authenticate the user before editing its crontab file. 
sys-process/htop:openvz - Enable openvz support
sys-process/htop:vserver - Enable vserver support
sys-process/procps:n32 - Enable n32 ABI support on mips
virtual/mpi:romio - Enable romio, a high-performance portable MPI-IO
www-apache/mod_mono:aspnet2 - Handle all applications using ASP.NET 2.0 engine by default
www-apache/mod_nss:ecc - enable Elliptical Curve Cyptography
www-apache/mod_security:perl -  Add a dependency upon Perl and install the script to update the Core Rule Set. Please note that this script will use the original Core Rule Set, and it's currently mostly untested. 
www-apache/mod_security:vanilla -  Provide the original ModSecurity Core Rule Set without Gentoo-specific relaxation. When this flag is enabled, we install the unadulterated Core Rule Set. Warning! The original Core Rule Set is draconic and most likely will break your web applications, including Rails-based web applications and Bugzilla. 
www-apache/mod_suphp:checkpath - Check if script resides in DOCUMENT_ROOT
www-apache/mod_suphp:mode-force - Run scripts with UID/GID specified in Apache configuration
www-apache/mod_suphp:mode-owner - Run scripts with owner UID/GID
www-apache/mod_suphp:mode-paranoid - Run scripts with owner UID/GID but also check if they match the UID/GID specified in the Apache configuration
www-apache/mod_vhs:suphp - Enable www-apache/mod_suphp support
www-apache/modsecurity-crs:vanilla -  Provide the original ModSecurity Core Rule Set without Gentoo-specific relaxation. When this flag is enabled, we install the unadulterated Core Rule Set. Warning! The original Core Rule Set is draconic and most likely will break your web applications, including Rails-based web applications and Bugzilla. 
www-apache/pwauth:domain-aware - Ignore leading domain names in username (Windows compat)
www-apache/pwauth:faillog - Log failed login attempts
www-apache/pwauth:ignore-case - Ignore string case in username (mostly Windows compat)
www-apps/389-dsgw:adminserver - Install DSGW with Admin Server
www-apps/ampache:transcode - Install optional dependencies for transcoding support
www-apps/bugzilla:extras - Optional Perl modules
www-apps/bugzilla:modperl - Enable www-apache/mod_perl support
www-apps/egroupware:gallery - Install gallery2 port for eGW
www-apps/egroupware:icalsrv - Install iCal Server (eGroupware-iCalSrv)
www-apps/egroupware:jpgraph - Add dev-php5/jpgraph support
www-apps/egroupware:mydms - Install eGroupware-MyDMS
www-apps/gallery:netpbm - Add media-libs/netpbm support
www-apps/gallery:unzip - Add app-arch/unzip support for the archive upload module
www-apps/gallery:zip - Add app-arch/zip for the zip download module
www-apps/horde-passwd:clearpasswd - Enables cleartext password storage in the vpopmail files
www-apps/ikiwiki:extras - Installs additional modules used by ikiwiki plugins
www-apps/lxr:freetext - Adds support for freetext search using swish-e
www-apps/mediawiki:math - Ads math rendering support
www-apps/postfixadmin:extras - Install contributed scripts and plugins
www-apps/postfixadmin:tests - Install model unit tests
www-apps/postfixadmin:vacation - Install vacation.pl script and dependencies
www-apps/redmine:darcs - Enable support for dev-vcs/darcs
www-apps/redmine:git - Enable support for dev-vcs/git
www-apps/redmine:mercurial - Enable support for dev-vcs/mercurial
www-apps/redmine:openid - Enable support for OpenID
www-apps/redmine:passenger - Enable support for www-apache/passenger
www-apps/rt:lighttpd - Add www-servers/lighttpd support
www-apps/trac:i18n - Enable support for i18n with dev-python/Babel
www-apps/venus:django - Support for django template style to config files
www-apps/venus:genshi - Support for genshi style to config files
www-apps/venus:redland - Enable support for Redland RDF
www-apps/viewvc:cvsgraph - Add dev-vcs/cvsgraph support to show graphical views of revisions and branches
www-apps/viewvc:mod_python - Add www-apache/mod_python support
www-apps/viewvc:mod_wsgi - Add www-apache/mod_wsgi support
www-apps/viewvc:pygments - Add dev-python/pygments support for syntax highlighting
www-client/chromium:gecko-mediaplayer - Allow the browser to load www-plugins/gecko-mediaplayer
www-client/chromium:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
www-client/chromium:system-v8 - Use the system-wide dev-lang/v8 installation
www-client/elinks:bittorrent - Enable support for the BitTorrent protocol
www-client/elinks:finger - Enable support for the finger protocol
www-client/elinks:gopher - Enable support for the gopher protocol
www-client/elinks:mouse - Make elinks to grab all mouse events
www-client/epiphany:nss - Import passwords from older gecko based www-client/epiphany keyring.
www-client/firefox:custom-optimization - Fine-tune custom compiler optimizations
www-client/firefox:ipc - Use inter-process communication between tabs and plugins. Allows for greater stability in case of plugin crashes
www-client/firefox:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
www-client/icecat:custom-optimization - Fine-tune custom compiler optimizations
www-client/icecat:ipc - Use inter-process communication between tabs and plugins. Allows for greater stability in case of plugin crashes
www-client/icecat:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
www-client/luakit:helpers - Optional tools used by luakit
www-client/lynx:gnutls - Use gnutls library for HTTPS support (openssl is the default library for HTTPS support).
www-client/lynx:ssl - Enable HTTPS support.
www-client/midori:html - Install HTML documentation, requires dev-python/docutils
www-client/midori:unique - Optional libunique support
www-client/midori:vala - Enable support for dev-lang/vala based extensions
www-client/opera:gtk - Set runtime dependencies to support GTK+/GNOME desktop integration
www-client/opera:kde - Set runtime dependencies to support KDE desktop integration
www-client/seamonkey:chatzilla - Build Mozilla's IRC client (default on)
www-client/seamonkey:composer - Build Mozilla's HTML editor component (default on)
www-client/seamonkey:custom-optimization - Fine-tune custom compiler optimizations
www-client/seamonkey:mailclient - Build Mozilla's Mail client (default on)
www-client/seamonkey:roaming - Build roaming extension support (default on)
www-client/seamonkey:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
www-client/uget:hide-temp-files - Make temporary files that are used while downloading hidden.
www-client/uzbl:browser - Install the uzbl-browser script
www-client/uzbl:experimental - Enable experimental branch
www-client/uzbl:helpers - Optional tools used by uzbl scripts
www-client/uzbl:tabbed - Install the uzbl-tabbed script
www-client/w3m:lynxkeymap - If you prefer Lynx-like key binding
www-misc/vdradmin-am:vdr -  Support for media-video/vdr. Disable this if the VDR you want to control runs at a remote machine. 
www-misc/xxv:themes - Enable more themes via x11-themes/xxv-skins
www-plugins/adobe-flash:32bit - For amd64-multilib, installs the 32-bit plugin
www-plugins/adobe-flash:64bit - For amd64-multilib, installs the native 64-bit plugin
www-plugins/adobe-flash:nspluginwrapper - For amd64-multilib, installs www-plugins/nspluginwrapper to allow use in a 64-bit browser. (Not recommended, see http://bugs.gentoo.org/324365)
www-plugins/gnash:agg - Rendering based on the Anti-Grain Geometry Rendering Engine library
www-plugins/gnash:cygnal - Enable building of the cygnal server
www-plugins/gnash:sdl-sound - Enable SDL audio output for the standalone player
www-plugins/gnash:ssh - Enable using SSH for network authentication in libnet
www-plugins/gnash:ssl - Enable directly using OpenSSL in libnet (not needed for nsplugin ssl support)
www-plugins/gnash:vaapi - Enables VAAPI (Video Acceleration API) for hardware decoding
www-plugins/moonlight:sdk - Enable building of monodevelop SDK
www-servers/apache:suexec - Install suexec with apache
www-servers/cherokee:admin - Install web based cherokee conf tool
www-servers/cherokee:coverpage - Installs the default cherokee coverpage
www-servers/cherokee:rrdtool - Enable rrdtool support
www-servers/fnord:auth - Enable HTTP authentication support
www-servers/lighttpd:libev - Enable fdevent handler
www-servers/lighttpd:memcache - Enable memcache support for mod_cml and mod_trigger_b4_dl
www-servers/lighttpd:rrdtool - Enable rrdtool support via mod_rrdtool
www-servers/lighttpd:webdav - Enable webdav properties
www-servers/nginx:addition - Enables HTTP addition filter module
www-servers/nginx:aio - Enables file AIO support
www-servers/nginx:flv - Enables special processing module for flv files
www-servers/nginx:http - Enable HTTP core support
www-servers/nginx:http-cache - Enable HTTP cache support
www-servers/nginx:libatomic - Use libatomic instead of builtin atomic operations
www-servers/nginx:pop - Enables POP3 proxy support
www-servers/nginx:random-index - Enables HTTP random index module
www-servers/nginx:realip - Enables realip module
www-servers/nginx:smtp - Enables SMTP proxy support
www-servers/nginx:static-gzip - Enables support for gzipping static content
www-servers/nginx:status - Enables stub_status module
www-servers/nginx:sub - Enables sub_filter module
www-servers/nginx:webdav - Enable webdav support
www-servers/ocsigen:ocamlduce - Enables ocamlduce XML typechecking for generated web pages
www-servers/pound:dynscaler - Enable dynamic rescaling of back-end priorities
www-servers/resin:admin - Enable Resin admin webapp
www-servers/tomcat:admin - Enable Tomcat admin webapp
x11-apps/xdpyinfo:dmx - Builds support for Distributed Multiheaded X x11-base/xorg-server
x11-apps/xinit:minimal -  Control dependencies on legacy apps (xterm, twm, ...). Safe to enable if you use a modern desktop environment. 
x11-apps/xsm:rsh - This allows the use of rsh (remote shell) and rcp (remote copy).
x11-base/xorg-server:dmx - Build the Distributed Multiheaded X server
x11-base/xorg-server:kdrive - Build the kdrive X servers
x11-base/xorg-server:tslib - Build with tslib support for touchscreen devices
x11-base/xorg-server:xorg - Build the Xorg X server (HIGHLY RECOMMENDED)
x11-drivers/ati-drivers:modules - Build the kernel modules
x11-drivers/ati-drivers:qt4 -  Install qt4 dependent optional tools (e.g Catalyst Control Panel) 
x11-libs/agg:gpc - Enable gpc polygon clipper library
x11-libs/cairo:cleartype - Add ClearType-style behavior for sub-pixel hinting. Patch taken from Arch Linux
x11-libs/cairo:drm - Use Linux DRM for backend acceleration
x11-libs/cairo:gallium - Use Mesa's Gallium backend for acceleration
x11-libs/cairo:glitz - Build with glitz support, which replaces some software render operations with Mesa OpenGL operations
x11-libs/cairo:lcdfilter - Add FreeType LCD filtering, ClearType-style behavior for sub-pixel-hinting. Overrides cleartype USE flag. Patch taken from Ubuntu
x11-libs/cairo:opengl -  When used along with USE=glitz, enables glitz-glx usage. Requires hardware OpenGL support 
x11-libs/cairo:openvg - Use OpenVG for backend acceleration
x11-libs/fltk:games - Builds and installs some extra games
x11-libs/gdk-pixbuf:introspection - Use dev-libs/gobject-introspection for introspection
x11-libs/gtk+:introspection - Use dev-libs/gobject-introspection for introspection
x11-libs/gtkdatabox:glade - Build with libglade and glade-3 supports, which includes a glade's module for GtkDataBox widget
x11-libs/gtkmathview:t1lib - Enable media-libs/t1lib support
x11-libs/gtksourceview:glade - Install a glade catalog file
x11-libs/libSM:uuid - Use UUID for session identification instead of IP address and system time. 
x11-libs/libdrm:libkms - Enable building of libkms, a library for applications to interface with KMS
x11-libs/libfm:demo - Build demo
x11-libs/libmatchbox:pango - Enable x11-libs/pango support
x11-libs/libmatchbox:xsettings - Enable the use of xsettings for settings management
x11-libs/libqxt:berkdb - Build the QxtBerkeley module
x11-libs/libqxt:sql - Build the QxtSql module
x11-libs/libqxt:web - Enable fast cgi bindings
x11-libs/libqxt:zeroconf - Build the QxtZeroconf module
x11-libs/libwnck:introspection - Use dev-libs/gobject-introspection for introspection
x11-libs/pango:introspection - Use dev-libs/gobject-introspection for introspection
x11-libs/qt:kde - Select media-sound/phonon as phonon variant needed for kde
x11-libs/qt:qt3support - Enable the Qt3Support libraries for Qt4
x11-libs/qt-assistant:compat - Build the extra compatibility package required by a few packages. More information at http://labs.qt.nokia.com/2010/06/22/qt-assistant-compat-version-available-as-extra-source-package/
x11-libs/qt-assistant:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-assistant:glib - Enable dev-libs/glib eventloop support
x11-libs/qt-assistant:qt3support - Enable the Qt3Support libraries for Qt4. Note that this does not mean you can compile pure Qt3 programs with Qt4.
x11-libs/qt-assistant:trace - Build the qttracereplay utility which is required to play drawings recorded with the trace graphicssystem engine
x11-libs/qt-core:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-core:glib - Enable dev-libs/glib eventloop support
x11-libs/qt-core:jit - Enables JIT for Javascript usage inside Qt
x11-libs/qt-core:optimized-qmake - Enable qmake optimization
x11-libs/qt-core:private-headers - Install Qt declarative private headers required by Qt-creator QmlDesigner and QmlInspector plugins"
x11-libs/qt-core:qt3support - Enable the Qt3Support libraries for Qt4. Note that this does not mean you can compile pure Qt3 programs with Qt4.
x11-libs/qt-dbus:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-declarative:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-declarative:private-headers - Install Qt declarative private headers required by Qt-creator QmlDesigner and QmlInspector plugins"
x11-libs/qt-declarative:qt3support - Enable the Qt3Support libraries for Qt4. Note that this does not mean you can compile pure Qt3 programs with Qt4.
x11-libs/qt-demo:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-demo:qt3support - Enable the Qt3Support libraries for Qt4. Note that this does not mean you can compile pure Qt3 programs with Qt4.
x11-libs/qt-gui:egl - Use EGL instead of default GLX to manage OpenGL contexts on the desktop
x11-libs/qt-gui:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-gui:glib - Enable dev-libs/glib eventloop support
x11-libs/qt-gui:private-headers - Install Qt declarative private headers required by Qt-creator QmlDesigner and QmlInspector plugins"
x11-libs/qt-gui:qt3support - Enable the Qt3Support libraries for Qt4. Note that this does not mean you can compile pure Qt3 programs with Qt4.
x11-libs/qt-gui:raster - Use the alternative raster graphicssystem as default rendering engine
x11-libs/qt-gui:trace -  Build the new 'trace' graphicsssytem engine which allows to record all drawing operations into a trace buffer. Later it can be replayed with the qttracereplay utility 
x11-libs/qt-multimedia:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-opengl:egl - Use EGL instead of default GLX to manage OpenGL contexts on the desktop
x11-libs/qt-opengl:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-opengl:qt3support - Enable the Qt3Support libraries for Qt4
x11-libs/qt-phonon:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-qt3support:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-qt3support:kde -  Select media-sound/phonon as phonon variant needed for kde 
x11-libs/qt-qt3support:phonon -  Enable phonon configuration dialog in qtconfig 
x11-libs/qt-script:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-script:jit - Enables JIT for Javascript usage inside Qt
x11-libs/qt-script:private-headers - Install Qt declarative private headers required by Qt-creator QmlDesigner and QmlInspector plugins"
x11-libs/qt-sql:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-sql:qt3support - Enable the Qt3Support libraries for Qt4
x11-libs/qt-svg:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-test:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-webkit:exceptions - Add support for exceptions - like catching them inside the event loop (recommended by Nokia)
x11-libs/qt-webkit:jit - Enables JIT for Javascript usage inside Qt
x11-libs/qt-webkit:kde -  Select media-sound/phonon as phonon variant needed for kde 
x11-libs/vte:glade - Provide integration with dev-util/glade.
x11-libs/vte:introspection - Use dev-libs/gobject-introspectionfor introspection
x11-libs/wxGTK:gnome -  Use gnome-base/libgnomeprintui for printing tasks. 
x11-libs/wxGTK:gstreamer -  Enable the wxMediaCtrl class for playing audio and video through gstreamer. 
x11-libs/wxGTK:sdl -  Use Simple Directmedia Layer (media-libs/libsdl) for audio. 
x11-misc/bmpanel:libev - Use the libev event loop interface
x11-misc/bmpanel:libevent - Use the libevent event loop interface
x11-misc/etm:ical - Enable export of ical format files by depending on dev-python/icalendar
x11-misc/fbpager:xrender - Enable transparency support via x11-libs/libXrender
x11-misc/google-gadgets:soup - Enables XML HTTP request extension based on net-libs/libsoup
x11-misc/google-gadgets:webkit - Enables browser element and script runtime based on net-libs/webkit-gtk
x11-misc/lightdm:consolekit - Enables support for authorization using consolekit
x11-misc/lightdm:introspection - Use dev-libs/gobject-introspection for introspection
x11-misc/lightdm:webkit - Build greeter based on net-libs/webkit-gtk
x11-misc/rednotebook:libyaml - enable libyaml support
x11-misc/rednotebook:webkit - enable previews using webkit engine
x11-misc/rss-glx:quesoglc - Enable support for OpenGL Character Renderer
x11-misc/shutter:drawing - Enables drawing tool
x11-misc/shutter:webphoto - Enables screenshots of websites
x11-misc/tint2:battery - Enable battery status plugin
x11-misc/tint2:examples - Install tint2rc examples
x11-misc/tint2:tint2conf - Build/Install tint2conf as well
x11-misc/vnc2swf:x11vnc - Install script that depends on x11vnc
x11-misc/x11vnc:system-libvncserver - Build x11vnc against the system libvncserver (experimental)
x11-misc/xlockmore:xlockrc - Enables xlockrc for people without PAM
x11-misc/xmobar:mail - Support the mail plugin. Pulls dependency dev-haskell/hinotify.
x11-misc/xscreensaver:new-login - Enable New Login button using gdmflexiserver (gnome-base/gdm) or kdmctl (kde-base/kdm)
x11-misc/zim:screenshot - Enable screenshot support (using media-gfx/scrot)
x11-plugins/bfm:gkrellm - Enable building of app-admin/gkrellm module
x11-plugins/compiz-plugins-extra:gconf -  Install GConf schemas for the plugins, needed when using the GConf-based configuration backend in x11-wm/compiz. 
x11-plugins/compiz-plugins-main:gconf -  Install GConf schemas for the plugins, needed when using the GConf-based configuration backend in x11-wm/compiz. 
x11-plugins/enigmail:custom-optimization - Enable user CFLAGS
x11-plugins/enigmail:system-sqlite - Use the system-wide dev-db/sqlite installation with secure-delete enabled
x11-plugins/gkrellmbups:nut - Enable monitoring Network-UPS via sys-power/nut
x11-plugins/purple-plugin_pack:talkfilters - Enable support for app-text/talklfilters
x11-plugins/screenlets:svg - Highly Recommended: Enable SVG graphics via dev-python/librsvg-python
x11-plugins/wmfire:session - Enable session management
x11-plugins/wmsysmon:high-ints - Enable support for monitoring 24 interrupts. Useful on SMP machines
x11-terms/aterm:background - Enable background image support via media-libs/libafterimage
x11-terms/aterm:xgetdefault - Enable resources via X instead of aterm small version
x11-terms/eterm:escreen - Enable built-in app-misc/screen support
x11-terms/hanterm:utempter - Records user logins. Useful on multi-user systems
x11-terms/mlterm:scim - Enable scim support
x11-terms/mlterm:uim - Enable uim support
x11-terms/mrxvt:menubar - Enable mrxvt menubar
x11-terms/mrxvt:utempter - REcords user logins. Useful on multi-user systems
x11-terms/rxvt:linuxkeys - Define LINUX_KEYS (changes Home/End key)
x11-terms/rxvt:xgetdefault - Enable resources via X instead of rxvt small version
x11-terms/rxvt-unicode:256-color - Enable 256 color support
x11-terms/rxvt-unicode:afterimage - Enable support for media-libs/libafterimage
x11-terms/rxvt-unicode:blink - Enable blinking text
x11-terms/rxvt-unicode:iso14755 - Enable ISO-14755 support
x11-terms/rxvt-unicode:wcwidth - Enable wide char width support
x11-terms/rxvt-unicode:xterm-color - Enable xterm 256 color support
x11-terms/xterm:toolbar - Enable the xterm toolbar to be built
x11-themes/gentoo-artwork:grub - Install extra sys-boot/grub themes
x11-themes/gentoo-artwork:icons - Install icons
x11-themes/gentoo-artwork:lilo - Install extra sys-boot/lilo themes
x11-themes/gentoo-artwork:pixmaps - Install pixmaps
x11-themes/gtk-engines-murrine:animation-rtl - Progressbar animation from right to left
x11-themes/gtk-engines-murrine:themes - Pull in themes via x11-themes/murrine-themes
x11-themes/gtk-engines-nodoka:animation-rtl - Progressbar animation from right to left
x11-themes/gtk-engines-qtcurve:firefox3 - Install GUI theme tweaks for version 3 of www-client/firefox 
x11-themes/gtk-engines-qtcurve:mozilla - Install GUI theme tweaks for mozilla based browsers, including version 2 of www-client/firefox 
x11-themes/qtcurve-qt4:kde - Enable KDE4 support. This adds a QtCurve configuration module to KDE's SystemSettings. 
x11-themes/qtcurve-qt4:windeco - Enable window decoration for KWin.
x11-themes/redhat-artwork:audacious - Install media-sound/audacious theme
x11-themes/redhat-artwork:cursors - Install Bluecurve cursors
x11-themes/redhat-artwork:gdm - Install Bluecurve gnome-base/gdm theme
x11-themes/redhat-artwork:icons - Install Bluecurve icons
x11-themes/redhat-artwork:kdm - Install Bluecurve kde-base/kdm theme
x11-themes/redhat-artwork:nautilus - Install Bluecurve gnome-base/nautilus icons
x11-themes/skinenigmang-logos:dxr3 - Install logos for lower osd color depth on dxr3 cards
x11-wm/compiz:fuse -  Enables support for the filesystem in userspace plugin through sys-fs/fuse. 
x11-wm/compiz:gconf -  Enable the GConf-based configuration backend; it is not required to work with GNOME, and might actually be faster if it's not used. 
x11-wm/compiz-fusion:emerald - Install the x11-wm/emerald package.
x11-wm/compiz-fusion:unsupported - Install the x11-plugins/compiz-fusion-plugins-unsupported package.
x11-wm/enlightenment:pango - Enable pango font rendering
x11-wm/enlightenment:xrandr - Enable support for the X xrandr extension
x11-wm/fluxbox:disableslit - Disables the fluxbox slit (or dock)
x11-wm/fluxbox:disabletoolbar - Disables the fluxbox toolbar
x11-wm/fluxbox:newmousefocus - Patches the focus model to the upcoming 1.1.2 model, which adds a new 'StrictMouseFocus' mode
x11-wm/fluxbox:slit - Enables the fluxbox slit (or dock)
x11-wm/fluxbox:toolbar - Enables the fluxbox toolbar
x11-wm/fvwm:gtk2-perl - Enable GTK2 Perl bindings
x11-wm/fvwm:lock - Enable screen locking
x11-wm/fvwm:netpbm - Enable NetPBM support (used by FvwmScript-ScreenDump)
x11-wm/fvwm:rplay - Enable rplay support
x11-wm/fvwm:stroke - Mouse Gesture support
x11-wm/matchbox-common:pda - Support for pda folders
x11-wm/matchbox-desktop:dnotify - Use the linux kernel directory notification feature.
x11-wm/matchbox-panel:dnotify - Use the linux kernel directory notification feature.
x11-wm/matchbox-panel:lowres - Optimize for low resolution screens.
x11-wm/musca:apis - Optionally install the experimental `apis' window manager
x11-wm/musca:xlisten - Optionally install the xlisten utility
x11-wm/openbox:session - Enables support for session managers
x11-wm/ratpoison:history - Use sys-libs/readline for history handling
x11-wm/sawfish:pango - Enable pango support
x11-wm/stumpwm:clisp - Use CLISP for the runtime
x11-wm/stumpwm:sbcl - Use SBCL for the runtime
x11-wm/vtwm:rplay - Enable rplay support, needed for sound.
x11-wm/windowmaker:modelock - Enable XKB language status lock support. README says: "If you don't know what it is you probably don't need it."
x11-wm/windowmaker:vdesktop - Enable dynamic virtual desktop (conflicts with software that works on the edges of the screen)
xfce-base/libxfce4ui:glade - Build support for Glade 3's GtkBuilder implementation
xfce-base/libxfcegui4:glade - Build glade bindings
xfce-base/xfce-utils:lock - Enable screen locking
xfce-base/xfce4-session:fortune - Install tips and tricks app (xfce4-tips), adds dependency on games-misc/fortune-mod
xfce-base/xfce4-session:gnome-keyring - Support for storing your password.
xfce-base/xfce4-settings:keyboard - Enable Keyboard layout selection with x11-libs/libxklavier
xfce-base/xfce4-settings:sound - Enable sound event support with media-libs/libcanberra
xfce-base/xfdesktop:thunar - Build support for desktop icons (for example, launchers and folders)
xfce-extra/thunar-thumbnailers:grace - Enable support for sci-visualization/grace thumbnails
xfce-extra/thunar-vcs-plugin:git - Enable dev-vcs/git support
xfce-extra/xfce4-mpc-plugin:libmpd - Build using media-libs/libmpd backend, instead of native fallback which is preferred
xfce-extra/xfce4-notifyd:libsexy - Enable support for clickable URLs by using x11-libs/libsexy
xfce-extra/xfce4-playercontrol-plugin:audacious - Enable Audacious support
xfce-extra/xfce4-playercontrol-plugin:mpd - Enable Music Player Daemon support