Drake 3D
Drake is a 3D data visualization tool, specializing in the display of robotically collected point, range, and volumetric data. Written in Python using PyOpenGL with critical sections written in C using scipy.weave, Drake provides a very flexible framework for different file formats and visualization parameters. One of the more exotic file formats is the Deferred Reference Count Octree described here.
A few screenshots.
Sourceforge project page
Code is available from the subversion repository. Example data and a Mac OS X alpha release is available here.