Leonardo da Vinci designed the viola organista as a stringed keyboard instrument operated by keys and a rotating friction wheel.
Leonardo’s surviving notebooks show several versions of the idea. Pressing a key selected a string, while a continuously rotating wheel rubbed against it to produce sound. This combined the keyboard’s ability to play several notes with the sustained tone associated with bowed instruments.
The viola organista was never completed as a working Renaissance instrument by Leonardo, so it is a design rather than a documented successful invention of his lifetime. Its name reflects the blend of viola-like sound and organ-like keyboard control, not a claim that it was an actual pipe organ.
Modern builders have constructed playable reconstructions from Leonardo’s drawings. The concept is sometimes confused with the hurdy-gurdy, which also uses a wheel rubbing strings, but the viola organista is controlled from a keyboard and was conceived as a more complex polyphonic instrument.