Leonardo da Vinci designed the viola organista as a keyboard instrument that produces sound with bowed strings.
The design uses keys to press strings against a rotating wheel fitted with horsehair or other bowing material. This combines the keyboard layout of an organ or harpsichord with the sustained tone of a bowed string instrument.
Leonardo drew several versions in his notebooks, but there is no evidence that he completed a working instrument during his lifetime. The idea was unusual because most keyboard instruments of the period plucked or struck strings rather than bowing them.
The viola organista is sometimes confused with the hurdy-gurdy, which also uses a rotating wheel, but the hurdy-gurdy is played with a hand crank and keys while the viola organista is operated from a keyboard.