Check out Cello Fortress, a weird and wonderful game from designer Joost van Dongen. In the video above you'll see how a live cellist plays notes on a cello and attacks others in the game at the same time. The game hears different performance nuances and uses those to determine what kind of attacks are used. For example, notes that are higher in pitch and played quickly trigger machine guns. Fast and high cords trigger double machine guns.
It seems the goal is to have the cellist doing double time, both fighting in the game and putting together a proper musical performance. That can't be easy, I'm sure. But wouldn't it be amazing to watch?
Watch how this cello controls a video game [Gamasutra]