What unusual keyboard instrument did Leonardo da Vinci design?

The viola organista was the unusual keyboard instrument designed by Leonardo da Vinci.

Leonardo developed several versions of the instrument during the late fifteenth and early sixteenth centuries. It combined a keyboard with a set of strings and a rotating wheel. When keys were pressed, the wheel rubbed against the strings, producing sustained tones in a way that combined features of a bowed string instrument and a keyboard.

The design appears in Leonardo's notebooks, including the Codex Atlanticus. It was not a conventional organ because it did not use pipes and air, and it was not a normal viola because the performer controlled pitch through keys rather than a bow and fingerboard.

No instrument built by Leonardo survives, but modern makers have constructed playable versions based on his drawings. The viola organista is often confused with the wheel fiddle, a different family of instruments in which a hand-turned wheel rubs against strings while keys select notes.