Open-source engine for Heroes of Might and Magic III
Open source clone of the Age of Empires II engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
A cross-platform 2D game engine
A fast, scalable, distributed game server engine/framework for C++
2D game engine for traditional platform games
A C++ 3D game engine.
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
Cross-platform 2D game engine