Aside from the numerous piano apps, there’s also String Trio, which basically “lets you play your iPhone [iPod Touch] like it was a violin, viola or cello.” It’s available now from the app store, priced at $1.99. Video demonstration after the break.
The music loads in, plays based on the strokes of the virtual ‘bow’. String Trio uses the motion sensor in your iPhone to detect the angle and length of your strokes, and adjusts the playback of the music accordingly.
[via Technabob]