Zombie Nation MUD (ZNMud) is a Multi-User Dungeon engine. It is based on the Teensey engine for its lower level socket handling. It was designed to play out zombie outbreak ideas but can easily be expanded to host other concepts. It's a massive multi-player text-based game (although it does support MXP). It also supports modern day weapons, etc.
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.
Mooix is a multiuser object-oriented dimension (a MOO) layered over top of your favorite Unix system. To the user, mooix looks much like any other MOO. To the programmer, mooix objects look like directories full of files: executable methods, properties, and links to other objects. MOOs have historically had poor support for such things as real programming languages, encrypted logins, multitasking, and editors. Mooix inherits all of these things from the Unix system it is based on. At the same time, it's not wedded too tightly to Unix (e.g., it implements its own permissions system that is much more suited to a MOO environment than the historical Unix system).
Multi-User Environment Server (MUES) is a multi-threaded, event-driven Internet game environment server written in Ruby. It is intended to facilitate the building of online multi-player games or simulations, by providing one or more dynamically programmed object environments (worlds), the means to access these environments (using a network client), various useful services or daemons (for creating in-game systems), and an event system (for facilitating the interaction of all the parts).
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.