As a radical new two-string violin goes on display in New York..............
https://www.youtube.com/watch?v=BmBizkOa5v4 (https://www.youtube.com/watch?v=BmBizkOa5v4)
http://www.youtube.com/watch?v=32emJq7MVsQ&feature=youtube_gdata_player (http://www.youtube.com/watch?v=32emJq7MVsQ&feature=youtube_gdata_player) I see your two strings and raise (well, lower) you...
And don't forget about the ol' diddley bow, which isn't much more than a single length of wire nailed to a flat board and has been around since the 1930s in America, and probably much longer in West Africa. Here's Seasick Steve puttin' his to good use:
https://www.youtube.com/watch?v=JPOMYHKWGTE (https://www.youtube.com/watch?v=JPOMYHKWGTE)
Eventually this thread will reach its ultimate conclusion with the mouth harp, (otherwise known, slightly racistly, as a Jew's Harp). Oh wait, it just did.