This is my first incarnation of a rigid body/physics demo based on the relatively new paper "Non-convex rigid bodies with stacking" by Eran Guendelman, Robert Bridson and Ronald Fedkiw. You can find the paper here and some slides here.
The current version (23 Feb 2004) of this demo handles box stacking, tetrahedrons, ellipsoids, cylinders, and rag-dolls (ellipsoids linked together with various constraints), and contains a sleeping algorithm for inactive objects. There are batch files to run it in three "demos": a rolling ragdoll, lots of cars + box stacking. Edit the config files to tweak these, especially if they run a bit slow on your machine. It can also be set up to run as a screensaver (quite nice with the ragdoll/car demos).
At some point I'll add some details. For now you can download the demo executable and source code (including MSVC6.0 project file, and Makefile for linux etc) here. Feel free to email me if you want to ask anything about it.