Ah, such fun: an evening wandering around the Wikipedia. Lots of cool stuff:
- The Official Berkely Breathed Website, homepage of the author of Opus.
- Pingus and Mormels (Marmets), both after Lemmings, the latter in Dutch.
- GNU Robots "is a game/diversion where you construct a program for a little robot, then watch him explore a world."
- LillyPond, a music typesetting tool similar to LaTeX; Denemo, an associated 'What You See Is What You Mean' GUI; and Project Mutopia, a free music archive (similar to Project Gutenberg, which is for books) which offers music in PDF, Postscript, and LillyPond format.