Free, cross-platform 2D game engine powered by Haxe and OpenFL
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Open source library for creative expression on the web, desktop, etc.
Open-source, cross-platform, C++ game engine for creating 2D/3D games
Modern AS3 Game Engine
3D .NET engine for Windows, Linux, Mac
PixelLight is a cross-platform application framework