Spineless is a generic cross-platform 3D game engine implemented in Python. Focus is on flexibility, clean design and ease of use, not pure speed or bleeding edge graphics.
MayaVi is a free, crossplatform, easy to use scientific data visualizer. It provides a GUI to ease the visualization process, is written in Python and uses the Visualization Toolkit (VTK) for the graphics.
Plasmatic is a crossplatform multimedia delivery and playback system. While designed primarily for digital signage applications, its flexibility allows for any number of uses.
...Can overlay images, xy-data, and mathematical functions. Function parameters can be tuned with sliders; functions can also be automatically fitted to data. Written in Python, cross-platform, but currently broken
The Pretty Poly 3D Modeller is a project to produce a free, powerful 3D modeller for Linux primarily, but built for cross-platform from the start. Since Pretty Poly loads and saves in many different 3D file formats, it is also a useful model format conver
BLIX is a cross-platform set of Python extension modules and Python scripts for Blender (www.blender.org). These scripts add camera calibration, 3D reconstruction and rigid body orientation to Blender.
Xgdk is a Cross-Platform Game Development toolKit. Its purpose is to provide a set of easy-to-use and extendable libraries for rapid development of 3d interactive applications such as videogames, demos and prototypes.
PyDemeter is a Python wrapper for the Demeter terrain engine, a cross-platform terrain rendering engine that uses advanced techniques such as dynamic tessellation to render complex landscapes at high frame rates. It can be used in conjunction with PyOSG,
A python module providing a cross-platform and cross-media drawing toolkit. It handles lines, polygons, curves, figures, and text--powerful enough for professional plotting--including support for wxWindows, Tk, Quickdraw, PDF, Postscript, and PIL.