iconv - Enable support for the iconv character set conversion library
mozsha1 - Makes git use an optimized SHA1 routine from Mozilla that should be fast on non-x86 machines.
perl - Adds optional support/bindings for the Perl language
ppcsha1 - Make use of a bundled routine that is optimized for the PPC arch.
python - Adds optional support/bindings for the Python language
subversion - Include git-svn for dev-vcs/subversion support.
test - Workaround to pull in packages needed to run with FEATURES=test. Portage-2.1.2 handles this internally, so don't set it in make.conf/package.use anymore
threads - Adds threads support for various packages. Usually pthreads