"The Irrlicht Engine is a high performance open source and cross platform 3D engine for creating realtime 3D applications. Its main targets are to be easy to use, extremely fast, extensible and crash safe.
The engine is a quite flexible graphics engine, and it is possible to write lots of different applications with it. Some are: complex 3D simulation applications, first and third person shooter games with indoor and/or outdoor scenes, real time strategy games, 2D games, ..."

License: free