The Tiny JavaScript Game Engine That Can!
A dead simple 2D game engine for Go
Xash3D FWGS engine
Voxel game engine in C++ with OpenGL
Open source library for creative expression on the web, desktop, etc.
2D game development library for Ruby and C++
A hand-crafted 2D game library in Go
A 2d physics game engine for JavaFX
Mahasona engine is an open source game engine.
A free ActionScript 3 library designed for developing 2D Flash games
Cross-platform 2D game engine