dbus - Enable dbus support for anything that needs it (gpsd, gnomemeeting, etc)
debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
grpc - Use net-libs/grpc to enable remote control capabilities.
ice - Use dev-libs/Ice to enable remote control capabilities.
pch - Enable precompiled header support for faster compilation at the expense of disk space and memory (>=sys-devel/gcc-3.4 only)
test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
zeroconf - Support for DNS Service Discovery (DNS-SD)
