In the Codex Atlanticus of Leonardo da Vinci, there is a drawing of a strange instrument called "Viola Organista" which dates from 1488 probably. This is a keyboard instrument that offers a sound like a viol. The idea is ingenious: a system of wheels with horsehair is fixed for rub the taut strings. Under the action of a key, the sound begins to vibrate, result of friction. The expression of this instrument is impressive because the player can play Crescendo on a keyboard!
Leonard did never have built his idea and the first traces of such an instrument back to the early 17th century. Today there is a single copy dating from 1625 kept in MIM (Musee des instruments de musique / Brussels). And even today, there is a single virtual copy, available here in MIB (Musee des instruments de Boscomac / Web), for you, friends of the Baroque.
Note that the string attack is proportional to the technique used : pianissimo for a slow and soft attack, staccato for a lively and rich attack. Also, the Crescendo / Vibrato is controlled with aftertouch keyboard.