Wikipedia
StumpWM
StumpWM is a tiling window manager that was created when developer Shawn Betts found ratpoison growing increasingly large and " lispy". Intended as a successor to ratpoison, StumpWM is released under the terms of the GNU General Public License, version 2 (GPLv2).
As explained on the StumpWM wiki, the developers decided to largely re-implement ratpoison in Common Lisp using CLX:
The authors describe StumpWM in the following terms: