Wintergarten Marble Machine (Programmable Instrument Using Marbles)

The creator (and musician) also made two videos explaining the inner workings (which is really cool from an engineering standpoint IMO):

* Part 1: https://www.youtube.com/watch?v=uog48viZUbM

* Part 2: https://www.youtube.com/watch?v=p0Guq7vZb_E