Magic Another Game Engine
The Tiny JavaScript Game Engine That Can!
Python MUD/MUX/MUSH/MU* development system
Full featured MUD server with all the trimmings.
Free, open source game engine online
The multiplayer game engine
3D playground built on three.js and cannon.js
A cross-platform 2D game engine
A mobile game distributed server implemented using netty4.X
Java decentralized cross-platform network multiplayer game engine
Educational framework for OpenGLES, OpenCL and OpenAL
Java Client + JS/Canvas Server-Side System, with maintained Objects
Free MMORPG Engine. Develop and host graphical browser-based games.