A bit tangential, in relation to MUD-like games and Lisp. The original author of co2 (that is to say before it was developed further by OP), has worked on a multi-user interactive fiction with some of the other persons who worked on this NES game. For that he used mzscheme to run a server side virtual world of bots/NPC interacting with the players via a browser/javascript client.

You can find some information there:

https://archive.bleu255.com/nakedonpluto/about/

https://gitorious.org/naked-on-pluto/game-server (cert expired)

https://gitorious.org/naked-on-pluto/game-client (cert expired)