If you want to watch a talk about the MUD that ActivityPub's original test suite was semi-derived from, here's one I gave, scroll down a bit. There's some cool ideas in there, like the ability to update the world live https://www.gnu.org/software/8sync/

And here's a blogpost about it https://www.gnu.org/software/8sync/news/mudsync-lisp-game-jam.html

You may notice that time is very shortly before ActivityPub's test suite came out, and that's no coincidence. I didn't have a lot of time, and i needed to borrow a lot of things