Played like a piano, sounds like a string quartet and invented by Leonardo da Vinci in 1470 though never built by him. From the youtube notes:
The invention of Da Vinci brought back to life in Krakow!
Viola organista was designed by Leonardo himself. The instrument seemed outstandingly promising, it fascinated Liszt and Bach’s son composed some works especialy on it. But then it misteriously vanished in mists of time… Until one Cracovian rebuilt it.