py3d is a Python-based procedural modelling and animation tool for building 3D scenes. It's fun to play with and even useful for teaching 3D geometry and transformations.
It's also under constant development. Lighting and materials just got added, and texture mapping and keyboard/mouse handling will be Real Soon Now.
Latest version is 3.5.1 with changes, bugs, and plans.
Py3d is built on top of the SGI OpenGL Performer high performance scene graph library. You don't get full source code, but the demo version with full development libraries included is a free download.
The py3dview source includes a number of C++ libraries which you may find useful even if you don't want to use the Python stuff: