Leonardo da Vinci designed the viola organista, a keyboard instrument with bowed wheels.
The viola organista combines features of a keyboard and a bowed string instrument. Pressing keys would select strings, while rotating wheels coated with friction material would rub against them and produce a sustained sound. Leonardo explored several versions of the idea in manuscripts, including the Codex Atlanticus and the Codex Madrid II.
Unlike a piano, the instrument was not designed around hammers striking strings. Unlike a violin, it could be played from a keyboard rather than with a handheld bow. Leonardo's purpose appears to have been to make the continuous tone of bowed strings available through a keyboard mechanism.
No surviving evidence shows that Leonardo completed a practical instrument. Several modern builders have reconstructed versions from his drawings, including a working instrument made by Polish instrument maker Sławomir Zubrzycki and presented publicly in 2013. The viola organista should not be confused with the hurdy-gurdy, which also uses a rotating wheel but normally has a crank and fingerboard.