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.
MV3D is a virtual world and multi-player game framework for use with Python. It was designed with scalability in mind and is able to distribute a world across as many servers as needed while dynamically balancing the load. The simulation framework is not specifically slanted towards any one genre of online game or virtual world, and can just as easily be used for a space game as a fantasy setting. Objects on an MV3D server can be simulated using the ODE physics engine for realistic interactions. A single server is able to host thousands of of simulated objects. The client works with both the Ogre3D and Panda3D renderers.
KMuddy is a MUD client powered by KDE. It aims to be the most powerful, fast, feature-rich and easy to use MUD client. The current version already offers many features such as powerful external scripting (which supports very many languages such as Python, Perl, Lua, and C/C++) and its own internal scripting. It has split-screen scrolling, command history, an auto-mapper, buttons, gauges, logging (both in plain text and HTML), multiple connections, regex support (on both aliases and triggers), and much more.
Gamma Low is a multi-player RTS in which two opposing teams of light-based lifeforms fight for the dominance over a cellular system in match style. The players in each team are split into different classes (strategist, tacticians, workers/attackers/supporters) and have to conquer all enemy cells in order to win. They do so by harvesting resources, building structures, researching technologies, creating deadly viruses, and fighting harsh battles.