Emacs denominates a class of powerful, extensible, self-documenting text editors. The original implementation is GNU Emacs, which is still updated today. There's also XEmacs, which was forked from GNU Emacs in the early 1990s. XEmacs is not the X version of Emacs, but a complete separate program.
Apart from the two big contenders, many lightweight implementations exist, many of which are available in Gentoo:
|Editor name||Gentoo package|
eselect repository enable emacs
emerge --sync emacs
layman -a emacs
Many more Emacs related packages should now be available for installation.