berkdb - Add support for sys-libs/db (Berkeley DB for MySQL)
bignum - Support for OpenSSL bignum implementation
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
dnd - Enables support for the x11-libs/dnd drag-n-drop library
eolconv - Support detection and translation of newline conventions
freewnn - Add support for FreeWnn kana to kanji conversion engine
gdbm - Add support for sys-libs/gdbm (GNU database libraries)