There is not yet an implementation of Emacs in CommonLisp. A lot of people would like to see one, however. It is often talked about on news:comp.lang.lisp. The McCLIM source includes the beginning of an Emacs in CL, but it’s not yet usable.
There’s also a page over on the Common Lisp Wiki on the subject. CLiki:CL-Emacs
Hmm, what about HemLock, the editor distributed with CMUCL? It is written in CommonLisp, and in the tradition of the WikiPedia:Lisp machine editor ZWEI and the ITS implementation, TecoEmacs. Includes a news and email client, can display to tty or X11. See http://www.cons.org/cmucl/hemlock/. – EricMarsden
Gilbert Baumann “ported” Hemlock to standard Common Lisp. The resulting project is called Phemlock, for Portable Hemlock.
Later, Climacs was created. Climacs is built on DREI, which is a combination meant to subsume both (Portable) Hemlock and Goatee.
See also: LiCE
There is also FRED (Fred Resembles Emacs Deliberately), which is an emacs implemented in CommonLisp. It comes with Macintosh Common Lisp, which means it is limited to running on Mac OS 9 or X on PPC machines.
Having used MCL and FRED I have to say FRED really stands for FRED Requires Extensive Debugging. The keybindings are also garbage and its attempt to be compatible with mac bindings just makes things worse. --sabetts