The Tiny JavaScript Game Engine That Can!
Open source clone of the Age of Empires II engine
Magic Another Game Engine
Python MUD/MUX/MUSH/MU* development system
The multiplayer game engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
3D playground built on three.js and cannon.js
A cross-platform 2D game engine
Java decentralized cross-platform network multiplayer game engine
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
Java Client + JS/Canvas Server-Side System, with maintained Objects