nls - Add Native Language Support (using gettext - GNU locale utilities)
objc - Build support for the Objective C code language
objc++ - Build support for the Objective C++ language
openmp - Build support for the OpenMP (support parallel computing), requires >=sys-devel/gcc-4.2 built with USE="openmp"
test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
vanilla - Do not add extra patches which change default behaviour; DO NOT USE THIS ON A GLOBAL SCALE as the severity of the meaning changes drastically