What instrument did Leonardo da Vinci design with a keyboard and rotating horsehair wheels?

Leonardo da Vinci designed the viola organista, a keyboard instrument with rotating wheels that rubbed strings like a bow.

The viola organista combined features of a keyboard and a bowed string instrument. Pressing keys selected strings, while a mechanism moved one or more wheels coated with horsehair or similar material against them. This arrangement aimed to produce sustained tones without requiring a performer to bow each string by hand.

Leonardo sketched several versions, but no surviving original instrument is known to have been completed by him. Modern builders have reconstructed working examples from his drawings. The instrument is not a piano: a piano strikes strings with hammers, while the viola organista produces sound through friction, closer to the principle of a violin or hurdy-gurdy.