On its surface, Cello Fortress looks like a fairly straight forward (if rudimentary) twin-stick shooter for up to five players. Dig just a tiny bit deeper, however, and you'll discover that this game has a somewhat unique set of rules. For starters, one of the players must always be a man named Joost van Dongen, and his controller absolutely has to be a cello. For realsies.
Basically, van Dongen controls the half of the game that would normally be the purview of the computer in a standard twin-stick shooter, spawning cannons and mines and such to thwart the other four players and their respective tanks. To do so, van Dongen must play his cello in varying ways, improvising melodies that will lead to both effective in-game strategies and a listenable performance.
Don't expect Cello Fortress to show up on Steam Greenlight anytime soon, though. The game is as much of a piece of performance art as it is a collection of code, and as such can only be experienced during live events scheduled by van Dongen. That schedule can be found on the game's official website, and here's hoping for some tour dates outside of The Netherlands.