I am not counting the Emacs Lisp implementations,
Interesting: I only know of one ELisp implementation
(https://github.com/mtk/teco/). I'd be interested if you
have pointers to other implementations.
as they are probably (?) only toys.
I don't know anyone who actually used it, but the description of changes
in the different "versions" suggests that it was definitely used by
some people. The README.md in the above Git repo suggests that the
current "maintainer" also uses it occasionally.
Stefan