Which Leonardo da Vinci invention was designed as a stringed keyboard instrument?

The viola organista was Leonardo da Vinci’s design for a stringed keyboard instrument.

Leonardo drew the instrument in the Codex Atlanticus and related notebooks during the late 15th century. Its keyboard controlled strings that were sounded by rotating wheels, combining features associated with bowed string instruments and keyboard instruments.

Unlike a conventional piano, the viola organista was not based on hammers striking strings. The player would press keys while a mechanism brought continuously moving, rosined wheels into contact with the strings, producing sustained tones.

Leonardo never completed a surviving historical instrument, but several modern builders have made working reconstructions. The name is commonly written in Italian as “viola organista,” not simply “viola,” which refers to a different bowed string instrument.