Questions related to the use of the Ogre 3D rendering engine and tools are appropriate for this tag.
Ogre 3D is an object oriented scene graph based engine. It has OpenGL and Direct3D support. The SDK is available on os x, linux and windows.
Offical website: http://www.ogre3d.org
Wikipedia entry: http://en.wikipedia.org/wiki/OGRE
Browse the source: https://bitbucket.org/sinbad/ogre/src