Global USE flags

Flag Description Packages
debug 2
doc 3
test Enable upstream build-time tests (requires Perl and optional Valgrind). 7

Local USE flags

app-emacs

telega

Flag Description
contrib Install miscellanous extra features
dbus Ensure Emacs supports dbus, for notifications
geo Enable geolocation support with app-emacs/geo
org Enable Org links
stickers Add support for animated stickers
texinfo Build and install Info documentation
tray Enable AppIndicator support

dev-games

tempest

Flag Description
audio
vulkan

dev-libs

gumbo

Flag Description
python

games-engines

gemrb

Flag Description
freetype
opengl
truetype

net-analyzer

hydra

Flag Description
firebird
gcrypt Enable radmin2 support through <pkg>dev-libs/libgcrypt</pkg>
gtk
idn
libssh Enable SSH support through <pkg>net-libs/libssh</pkg>
memcached
mongodb MongoDB support through <pkg>dev-libs/mongo-c-driver</pkg>
mysql
ncurses
oracle
pcre
postgres
rdp
samba
subversion
zlib

net-libs

tdlib

Flag Description
clang Compile using Clang
cli Install tg_cli
gcc Compile using GCC
java
low-ram Split source files during compilation (for systems with less than 3.5G RAM)
lto Enable Link Time Optimization