As for the 'composition', I started with a standard guitar tuning, but each string loops through a sequence of interval offsets from that tuning, advancing one step each time it gets hit. Not my favorite but it sort of works, I think.
Update: I added some ways to tweak the sound (stretch and damp) as well as the speed of the balls (dt). Up and down arrows select parameters, left and right change them. It's definitely more interesting this way.... For stretch and damp - low stretch values kill high frequencies faster, whereas low damp values tend to reduce all frequencies equally.