Emacs Common Lisp is an implementation of Common Lisp written in Emacs Lisp. That means you can run Common Lisp programs in Emacs, and you can write Emacs extensions in Common Lisp. At this stage, much of ANSI Common Lisp is implemented, but, among other things, CLOS and pretty printing are missing. For more information, see the README file.

There is a mailing list for discussion about Emacs Common Lisp. (Also accessible through Gmane.)

Browse the git repository here.

EmacsWiki page.