It was released 25 years and four days ago, and is still around. Simple enough to still work I'd bet, though the last official release was in 2017 or so.

https://www.nongnu.org/ratpoison/

http://savannah.nongnu.org/projects/ratpoison

I used it for a while back then, before switching to IceWM because it was more fun to configure. Prepared me well for a much later move to i3.