ErlyMUD is a rather minimalistic MUD server, written in Erlang and making use of the excellent OTP libraries. The aim is to have solid support for exploration and roleplaying, within a highly fault-tolerant environment where system crashes or reboots are more of an exotic curiosity than a commonplace thing.
Cancan is a text-based, interactive utility similar to telnet, but with a number of extensions useful for MUD playing. Another use might be to provide line editing, aliases, etc., for those services that have a simple telnet interface. Cancan features aliases, actions, key bindings, text highlighting, substitutions, and line editing with history and completion.
Lich is a cross-platform multithreaded interpreter meant exclusively for use with text-based MUDs. Its primary goal is to provide a dynamic and extensible framework that offers advanced users the ability to customize the application and its functionality to their needs while remaining accessible and useful to the majority of players. It supports scripting in Ruby, Simutronics "Wizard", and, in Unix environments, any language with an interpreter program.
LDMud is an LP-class MUD engine, meaning it is object-oriented, with all object clases stored in unique files. The engine runs compiled bytecode to manipulate those objects, and the underlying simulated processor is a stack machine. It is a 3rd-generation LP-class MUD, being derived from Amylaar, which in turn was derived from the original LPMud. The game has no limitations on the nature of the game space other than the limits of your coding.
AweMUD is a MUD server for use with fantasy-settings. Features include fully dynamic objects and characters, an advanced scripting system, and custom worlds. The engine will eventually have completely interactive rooms (items can be placed under benches, doors can be destroyed), complex magick, and interactive NPCs.