Don't spend all evening twiddling with weights and pendula. Your evening guests can be immediately entertained by the profusion of spiralia generated by the Harmonograph! Move the sliders to change the harmonograph output dynamically.
Interesting results can be obtained when just off a harmonic interval i.e. a 5th (F=3/2), unison (F=2/1) etc. Perhaps a visual representation of musical harmony...
Updated to include an App file for R2012b