Your Internet Consultant - The FAQs of Life Online
MUDs crossed the Atlantic around 1988 and gained popularity in the United States. As the New Hacker's Dictionary says, "[The] second wave of MUDs emphasized social interaction, puzzles, and cooperative world-building as opposed to combat and competition."
In 1992, more than 50 percent of MUD sites were of a third major variety, LPMUD, which combines the combat and puzzle aspects of AberMUD with extensibility. The trend toward greater programmability and flexibility has continued.
As programmers create new types of MUDs, new names appear for the environments. These include TinyMud, DUM, MOO, MUCK, MUG, and a plethora of others. Although some types of systems are generally used for a certain type of game, the best way to find out what a certain MUD is like is to just connect to it.