ErisMUD is a MUD/MOO server/engine written in Python and supports many features: rooms, NPCs, items, player skills and stats, ANSI colors, a help system, damage/healing, etc. SQLite is used to store the data, so no files are required for building (unlike LPMUDs). Short and easy internal commands take care of the development and maintenance.
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.
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.
Genecys is a massively multi-player online RPG. It is a completely dynamic environment. Each server is completely unique and follows its own progression of events. Maps will be generated randomly, at server startup, as will towns and NPCs. NPCs will be AI controlled, and have their own lives in the game, and exist to interact with the players, not just to be slaughtered by the players.