aqua - Include support for the Mac OS X Aqua (Carbon/Cocoa) GUI
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
eigen - Enable dev-cpp/eigen mathematical templates support
nls - Add Native Language Support (using gettext - GNU locale utilities)