RPG Maker 2000/2003 and EasyRPG games interpreter
High performance UI layout library in C
Orx: Portable Game Engine
Cross-platform 2D game engine (+ full OpenGL, +full OpenGL ES )
Old-school 2D game engine
mGSTEP port of the Cube game engine
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
TurboSphere is an easy to learn and powerful JS based game engine.
3D game engine for C and C++