[busseio]

TinyMUSH (which is somewhere between TinyMUD and TinyMUSE if my historic memory is correct): https://github.com/TinyMUSH/TinyMUSH

[cmrdporcupine]

Sure, or MOO.

Even better, a MOO (or any MUD) client in emacs (rmoo.el, mud.el etc), which is how I got my start with emacs eons ago.