The Bowed Piano

Source: Colorado College, Colorado Springs.

In case you were wondering, they're actually playing contemporary music on that piano.

In the viola department, there's PDQ Bach's Viola Sonata for Four Hands - yup, four hands, one viola. Two bows though. Well, at least for the outer movements... I seem to recall the directions calling for the use of fishing reel for another, and the option of sword-fighting with the bows as the exit of the violists - and the piano accompanist can leave when he/she realizes that the stage is empty.