Leonardo da Vinci designed the viola organista to make continuous music with bowed strings controlled by a keyboard.
Unlike a harpsichord, which plucks strings, or a piano, which strikes them, this instrument was intended to create sound by rubbing strings with a moving bowing mechanism. Keys would select the notes while the mechanical system supplied sustained friction.
Leonardo developed the idea during his investigations of musical instruments and mechanical motion. The surviving drawings are not a complete modern manufacturing manual, so builders have interpreted details differently when creating reconstructions.
The viola organista is sometimes described as an organ because of its keyboard and capacity for sustained sound, but it does not produce tones through organ pipes. It is also not simply a bowed piano: its defining feature is the mechanical bowing of strings, which gives the concept its distinctive place in instrument history.