Stump Window Manager
Current version (October 2003) is 0.0.3. I didn't try it.
I encountered this WM via a link from Ratpoison's web page. Stump is creating a behaviour very similar to Ratpoison (or Ion without titlebars) on a Common Lisp base. The code is so new that I opted not to try it out.
One mailing list, some recent activity, only about four posters.