PHIGS (Programmer's Hierarchical Interactive Graphics System)
Webgl Engine
A cross-platform game framework based on OpenGL and GObject.
Gimpel3D - 2D/3D Stereo Conversion Editor
Pear3DEngine is a modern and modular 3D development framework
Minimalist 3D Scenegraph Management Framework
Game engine supporting many 3D/2D formats and graphic effects