Leonardo da Vinci designed the viola organista, a keyboard instrument intended to make bowed strings sound continuously.
The concept used a keyboard to control strings while a rotating mechanism supplied the friction normally produced by a bow. This allowed a player to change notes with keys while maintaining a sustained, string-like sound. Leonardo produced several designs, but none is known to have been completed by him.
The instrument sits between familiar categories: it has a keyboard like an organ or harpsichord, yet its sound production resembles that of bowed string instruments. That combination makes it different from a standard viola, which is played directly with a bow.
Modern makers have built playable reconstructions from Leonardo’s drawings. Those reconstructions demonstrate the ingenuity of the concept, but they are modern interpretations rather than surviving Renaissance originals.