The Viola Organista was an invention dreamed up by Leonardo da Vinci. In 1993 and 2004 a couple of these were made. Now we have some great video of a man who built one and performed a concert. Below is the original drawing that Leonardo made over 500 years ago.
A Polish master instrument maker used the drawing as a basis for making the third ever Viola Organista. It uses rotating drums, wrapped with horse hair, as sort of an endless violin bow. The strings are pressed down onto the rotating drum when the key is pressed.
The thing sounds like the entire string section of an orchestra! It's really neat.
Music starts at about 4:00, and English subtitles are available by clicking "CC" at the bottom right, if you are interested in the interview part.
Below, the first time this instrument was ever heard in public.