This piano, created by a group of independent developers, plays Doom using the assorted keys. It's called the Doom Piano.

The white keys dictate movement, while the black keys handle shooting. The piano was recently on display at the Virgin Media Game Space in London. The piano was created by show organizer David Hayward, developer Sos Sosowski, Die Gute Fabrik's George Buckenham (Johann Sebastian Joust), and Honeyslug's Ricky Haggett (Hohokum). You can check out a video of someone playing the Doom Piano below.

I heard that if you play Beethoven's "Fur Elise" on the Doom piano, you can get through the entire game without losing any health.

[Source: Gamasutra]