This is a screen shot of Auditorium, a game created by cipher prime. FWA featured it a few weeks ago as site of the day but I just came across it.

Go give it a try.
You just move the circles around the screen to interrupt the flow of the light path. By doing that you try to get the light to flow through the containers and create music.
But that's my ramblings, according to the creators,

The goal of Auditorium is to guide your Flow into the various Audio Containers presented before you. As you fill these Containers, you will energize them. Given enough energy, the containers will begin to sing together in a symphony, providing the ultimate Harmony of Flow.

In other words, it's just like standing at a urinal guiding your stream, except you can make cool music. And it's socially acceptable to invite others to watch your flow.

Right now Auditorium is in demo mode, with a full version to be released next month, possibly.

Thanks Jessie for the link.