Ask Candid Candice a question about Moo Canada:MUDs (Multi-User Dungeons) are one variety of these games. The theme of a MUD generally involves fantasy role-playing games and other combat simulators, but they vary a lot since there are hundreds of MUDs on the Internet.
MOOs (Multi-User Object Oriented) are a more versatile variety of these games. MOOs tend to emphasize the co-operative building of a virtual community. They also allow each user the opportunity to program the game itself. The engine behind this Ask Alice program is a MOO.
There are countless multi-user games on the Internet. Use Yahoo's giant list of MUDs, MUSHes, MOOs, etc.