Orx: Portable Game Engine
Multi-platform game engine similar to old Megaman with a stage editor
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
A generic 2D engine for any kind of game
A basic 3D environment with a first-person POV
A Simple Game Engine
a flexible game engine
A very small multi-platform game engine for creating desktop games.
Reference implementation for the Doom game engine.