From the fortune file:
Campus sidewalks never exist as the straightest line between two points. -- M. M. Johnston
At rural colleges and similar settings, people form very distinct paths in the snow as they walk across open spaces. This program models this process of snow path formation. The evolving condition of the snow is displayed graphically. It runs at least on GNU/Linux, NetBSD and FreeBSD and hopefully on most other things with X. It can be run from xscreensaver.
For downloads, go to the Sourceforge project page.
More animated examples...
My other projects: l7-filter, protocolinfo.org, nosefart.