LPmud

LPmud came into existance as an attempt to do better than some existing MUDs. Basically AberMUD and TinyMUD were the base from which LPmud was written. It was from the very start completely different code though. The same style of playing was implemented but the core system was alot more flexible.

LPmuds are basically just an interpreter with a small runtime environment in it. The runtime environment takes care of some things like file access and network communications, and that is about it. All other aspects of the game are programmed in the interpreted language LPC (in real usually byte-compiled).

The popularity of LPmud is mostly a result of its flexibility, and its unique style. Two LPmuds are usually much more different than any other two MUDs using the same software.

One particular application of LPmud is the implementation of World Wide Web servers in LPmud (and LPmud-alike servers). They are written in the builtin LPC languages, and usually very object oriented. The following are known:

Roxen WWW server, originally developed by people at Lysator University in Sweden.
Nightmare WWW server

No other working applications are known, although there is a lot of research going on right now, about:

Accessing MUD information through WWW clients
Accessing information on the Web from within MUDs
Graphical user interfaces to MUDs