Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were rubbed continuously.
Leonardo’s sketches show a keyboard controlling mechanisms that press strings against a rotating wheel or wheels. The friction makes the strings vibrate, producing a sustained sound. The concept combines features associated with bowed string instruments and keyboard instruments, which is why the name refers to both the viola and the organ.
Unlike a normal piano, the player would not strike each string with a hammer. Unlike a conventional viola, the player would not move a bow by hand. Leonardo explored several versions of the idea, but no surviving instrument from his workshop proves that he completed a playable original.
Modern instrument makers have built reconstructions from the drawings. These reconstructions help demonstrate the principle, but they should not be mistaken for an original Leonardo instrument preserved from the fifteenth century.