I have made the following, to try to learn some odd programming languages.

• Aperiodic Celtic knot fridge magnets
  • Pattern 1 (pdf) (ps)
  • Pattern 2 (pdf) (ps)
  These are based on Penrose's kites and darts aperiodic tiling of the plane. They can be printed on an 8.5 x 11 sheet magnet, then painstakingly cut into individual tiles. They were created with metapost. (I do have a better design in the works, one which involves much easier cutting.)
• Balkan folk music
  • Done Mari (pdf) (midi) (ly)
  • Son Mi Dojde (pdf) (midi) (ly)
    origin
  These were typeset with lilypond

I recently acquired a semi-rare spoof of a math textbook, Mathematics Made Difficult, by Carl Linderholm. Here is an excerpt discussing the "rule of three" pp 142-143 pp 144-145