Emacs

Emacs denominates a class of powerful, extensible, self-documenting text editors. The original implementation still updated today is GNU Emacs, a derivative is XEmacs, which was forked from GNU Emacs in the early 1990s. The latter is not the X version of Emacs but a complete separate program.

Apart from the two big contenders, many lightweight implementations exist, a lot are available in Gentoo.

Overlays
The Emacs LISP project runs two overlays for GNU and XEmacs which contain a number of packages including many VCS builds. To add the overlay:

layman -a emacs or layman -a xemacs

Official Documentation
See http://www.gentoo.org/proj/en/lisp/emacs/emacs.xml