Leonardo da Vinci designed the viola organista, a keyboard instrument that used rotating friction wheels to sound strings.
Leonardo developed versions of the idea during the late 15th and early 16th centuries. Pressing keys would bring rotating wheels into contact with strings, producing sustained tones in a way that combined features of bowed string instruments and keyboard instruments.
Unlike a piano, which uses hammers, the viola organista relied on friction to make the strings vibrate. Unlike a conventional organ, it did not primarily use pipes and air. Leonardo’s surviving drawings show the concept, but no original instrument made by him is known to survive.
Modern builders have constructed working replicas based on the sketches. The name can be confusing because the instrument is not a standard viola and is not simply a modified piano; it is a distinct keyboard-operated string instrument.