HemLock is an extensible Emacs-like text editor embedded in CMUCL. It follows the tradition of the Lisp Machine editor ZWEI and the ITS/TOPS-20 implementation, TecoEmacs. Hemlock is supposed to be able to display to a terminal, or use CLX for X11; afaik only X works at present.
It is part of Debian:
In more recent versions of Debian it moved into the cmucl-source package.
Some people do seem to be actively hacking on Hemlock – see e.g. CLiki:CloserLookAtHemlock.