http://irrlicht.sourceforge.net/
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, ...
The engine is open source and totally free. You can debug it, fix bugs and even change things you do not like. And you do not have to publish your changes: The engine is licensed under the zlib license, not the GPL or the LGPL.
Have a look at it DEVs. Maybe this one could be useful four you and the future development of Hz :)