Appalachian dulcimer.

To assist the player, the frets only cover a major scale, a decision I can only assume is because the player can't handle the mental challenge of chromatic frets. So everyone has to play in the dulcimer's key if you want to give them a go, and even then the lack of chromatics usually means there's somewhere in the tune (especially on British Isles folk tunes that go modal in places) where everyone else is playing a semitone away from the dulcimer. There's only one melody string, so the only way of playing a tune is sliding up and down in search of the note. And its body size and shape limits it to the tinny buzz-and-twang of a Martin Backpacker. Thankfully it's also limited to the volume of a Martin Backpacker, so you can fairly easily drown it out with people who can play real instruments.

Graham.