What string instrument with a keyboard did Leonardo da Vinci design around 1488?

Leonardo da Vinci designed the viola organista, a keyboard instrument that produces sound from bowed strings.

Leonardo's surviving sketches show a keyboard connected to rotating wheels or bows. When a key was pressed, a string could be brought into contact with a continuously moving friction surface, allowing the player to produce sustained tones in a manner related to a viol.

The instrument combined features of a keyboard and a stringed instrument. It was not simply an organ: ordinary organs use pipes and air, while the viola organista relies on vibrating strings. Leonardo explored the concept in notebooks during the late fifteenth century.

No original Leonardo instrument is known to survive. Modern builders have made playable reconstructions from his drawings, although the sketches leave room for interpretation about the exact mechanism and layout.