Somehow I missed this when it went around in the beginning of the year. Regardless, it's fantastic. BallDroppings, by Josh Nimoy, is a highly addictive musical play toy based on the simple principles of the original computer game, Pong. By drawing lines you manipulate where dropping balls bounce, and with every bounce a musical note is played.
Be sure to check out jtnimoy.com for a glimpse of his other work. There's lots of fun and pretty stuff besides BallDroppings!