Alright, there are telnet text games, collectively known as Mu*s.
There are several codebases/servers types out there. These servers/codebases are used for general kind of game, with a presupposed Player culture.
Muck codebase/server, are inclined to be Adult and/or Furry in theme.
Muds, are generally player vs. players and players vs. mobs. These are the grand daddy for the modern MMO. They functional, pretty much identically really, except that its text base, and the playerbase is smaller. There are quests, and gear, all that jazz.- However, some Muds, like, Hellmoo, promote their players to be assholes to each other. Some Muds are heavy role playing games, other arent.
Mushes (Tiny, Penn, and Rhost)[They're sister codebases/servers.] These tend to be more social and/or rp focus. They also frown upon assholes on them.