A performant, flexible, and easy-to-use real-time 3D rendering engine
A public domain cross platform 3D game
3D .NET engine for Windows, Linux, Mac
A really simple (following K.I.S.S statement) ray tracing project.
PHIGS (Programmer's Hierarchical Interactive Graphics System)
Webgl Engine
an interactive 3D viewing program
A cross-platform game framework based on OpenGL and GObject.
Gimpel3D - 2D/3D Stereo Conversion Editor
3D game engine for C and C++
Pear3DEngine is a modern and modular 3D development framework
Minimalist 3D Scenegraph Management Framework