Gimpel3D - 2D/3D Stereo Conversion Editor
3D game engine for C and C++
3D world editor for game development
Pear3DEngine is a modern and modular 3D development framework
Minimalist 3D Scenegraph Management Framework
https://github.com/horde3d/Horde3D
Multi-Language Wrapper Collection for the Irrlicht Engine
PixelLight is a cross-platform application framework
A 3D rendering / entity engine
A C++ library to easily create GUI-editable objects
Bruno's RAY Tracing Engine