Full featured MUD server with all the trimmings.
Orx: Portable Game Engine
Game engine supporting many 3D/2D formats and graphic effects
An online multiplayer turn based strategy game and board game engine.
A multiplatform game engine for interactive fiction experiences
UtiliGame is a light-weight game engine written in Java.
Javascript adventure game engine
A game engine in java for 2D strategy games
Game engine supporting many 3D/2D formats and graphic effects
Free MMORPG Engine. Develop and host graphical browser-based games.