Technically speaking, any instrument could be considered "collaborative"--as anyone who's played "chopsticks" with a friend on a piano knows. But Matt West has stripped that notion down to its essence with his electronic "Collaborative Instrument," which consists of little more than a button to control rhythm, a knob to control pitch, and a speaker to hear the results. If Chang and Eng had been born as 21st-century chiptune geeks, they'd have loved this thing.
Each player holds one of two boxes, connected to the main unit by a cord. Then they play beautiful music together. (By which we mean, "weird noises that sound like telegraph signals or submarine sonar.")
Not exactly Mozart. Or "chopsticks," for that matter. But does it look fun? Hell yes. And you can't quibble with West's retro cabinet design.
If West puts as much effort into the actual tunes as he did into the physical design, this could end up being more fun than Rock Band at parties.