sys-block/mbuffer
M(easuring)buffer is a replacement for buffer with additional functionality (+ JRG race condition patch)
USE Flags
debug
Global: Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see http://www.gentoo.org/proj/en/qa/backtraces.xml
ssl
Global: Adds support for Secure Socket Layer connections
test
Global: 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