The Tiny JavaScript Game Engine That Can!
Full featured MUD server with all the trimmings.
Free, open source game engine online
State Management and Multiplayer Networking for Turn-Based Games
Retro game engine for creating games like it's 1997
3D playground built on three.js and cannon.js
A mobile game distributed server implemented using netty4.X
online 4X browser game engine
Pig2D is a game engine for Java that uses a sprite-based interface.
Cross-platform 2D game engine
Zap Engine