Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were sounded by a rotating wheel.
Leonardo recorded the concept in drawings from the late 15th century. Pressing keys would select strings while a hand-operated wheel, covered with horsehair or another friction material, continuously rubbed them. The result was intended to combine the keyboard's ability to play several notes with the sustained sound of bowed strings.
The viola organista was never a standard Renaissance instrument and Leonardo did not leave a fully functioning surviving example. Modern builders have reconstructed versions from his sketches, sometimes producing sounds resembling a viola, cello, or organ depending on the design.
It is often confused with a hurdy-gurdy because both use a wheel and strings. The important distinction is that the viola organista uses a keyboard to control the strings, whereas a hurdy-gurdy uses keys and a crank in a different mechanism.