This dulcimer isn't actually appalachian. It may be best-known today as being played there, but that's just an accident of history. The Scotch-Irish of the mid-south got it from the Pennsylvania Dutch, who came from the Rhineland. Since the Rhine goes through French and German lands, the dulcimer was probably known, if perhaps not well-known, in those regions. Before that, who knows?

It's just another member of the great zither group. You can tune it DAA or DAD and play in a major scale, or you can tune it DAG and play minor. (There are other tunings, but I don't know how to use them.) Just to show the variety it can play, I'll list a few of the tunes I do. These are DAA.

Salve Regina (1200's)
Never love thee more (1600's)
Polly-wolly doodle (1904)
Ascot Gavotte 1950's
Wildwood flower 1850
Yellow bird, up high in banana tree - Caribbean
When I fall in love, it will be forever (pop song)
The man on the flying trapeze - Tin Pan Alley
Peace in the Valley - bluesy

What's missing? Any popular stuff after 1980, when our radio died. Also, fast jigs and reels, which I personally find boring to play. I like to use a thumbpick to play the melody and keep my other fingers free to play various kinds of accompaniment. I can always strum if I want to, but if I don't want to, I'm free to play other ways.