Leonardo da Vinci designed the viola organista, a keyboard instrument using bowed strings.
The player would press keys, while a mechanism caused rotating wheels or a continuous moving bow to contact strings. This combined the controllable keyboard layout of an organ or keyboard instrument with the sustained, friction-produced sound associated with bowed strings.
Leonardo drew several versions of the mechanism in his notebooks. No surviving original instrument by Leonardo is known, but modern builders have constructed working interpretations from his drawings.
The viola organista is often confused with a hurdy-gurdy because both use friction to sound strings. Its defining feature is the keyboard control, which allows the performer to select pitches more like a keyboard player than a conventional bowed-instrument musician.