A couple of weeks ago, I was invited to an Alphalabs event where we were given the task of extending a project called NodeGarden. On the weekend, I spent an hour or so extending the project into what I call Note Garden. You can see of it below:
As you (possibly) saw, each 'node' has been converted into a musical note. When the marker comes across the screen, it detects which note it has hit and plays it. When the marker gets to the end of the screen, all the notes randomise and so you get a different tune each time.
I've made the source code available over at CodePlex.