To expand on MUD a little:
Also called Multi User Dimension (for those non-dungeon crawl games). Back then you didn't have the "world wide web", so the internet was mostly "telnet", along with a few other means of communication and file transfer (like Gopher, FTP, and UseNet). MUDs were all text based (think Zork), but unlike Zork and other text based games, you could interact with other players, there was a game "heartbeat" that meant that events could happen without you doing anything (yet you could still use basic turn based play), and the world was persistent. Someone could drop something in one "room" and when you walk in, it would be there. If you took it, they would no longer have access to it. This might sound really basic and simple, but at the time it was revolutionary.
At that point in technology, there was no such thing as a large scale multi-player game. You had a few choices for multi-player games:
- Turn based games on the same computer.
- 2 and 4 player consoles (same screen)
- LAN, serial, or modem based between two computers. (usually limited to 2 players)
- Games like Trade Wars, which were turn based games hosted on a BBS (bulletin board system, pre-internet site that you dialed into with a modem), where you would log in, take your turn, and then check back the next day to find out the results.
Then of course you had board games and card based games, and RPG's like D&D. But all those required everyone be in the same room at the same time. To suddenly be able to play with players from all over the world, in real time, with 50 players, was quite amazing (and quite addictive).
On top of this, you could become a programmer and write your own dungeons or even entire worlds that other players could play in. Most of the time you had to reach a certain level in the game, then apply to the game masters to get that access, and you had to know the programming language, which was really simple (very close to 'C').
MUDs were the predecessor to the modern MMO-RPG. Games like Ultima Online, Dark Age of Camelot, Everquest, and World of Warcraft are all "next gen" versions of a MUD.
FYI, Zork is available to play online by a slew of different sources. Some are like a MUD where you telnet in to play, some are just online as a PHP app, and some are Java based. For anyone who was into computer gaming back in the 80's played Zork, it is a great trip down memory lane..