I believe that mountain dulcimers and hammered dulcimers are among the world's coolest musical instruments. The general public deserves to know them the way it knows guitars and pianos.
The mountain dulcimer is similar to a guitar, except for a few of the particulars:
For years, I thought mountain dulcimers were relatively uninteresting -- after all, how much could you do with only 3 strings? But once I started playing it, I discovered that those supposed shortcomings actually are great strengths.
Think of it this way: A guitar has 6 strings and you have 5 fingers. You're outnumbered. A mountain dulcimer has 3 strings and you have 5 fingers. You don't have to worry about all those excess strings being in the way. A beginner can pick out songs fairly easily -- but, with practice, it's easy to play melody and accompaniment at the same time.
Dulcimers come from traditional folk roots, and I love traditional music, but they're also great for popular music. "The Folk" have always played popular music. However, before cars and radio, "popular" tended to be what your kin and your neighbors played.
My "standard" setup for a dulcimer includes 0+, 1+, and 8+ frets (and of course the 6+ and 13+, which are virtually standard nowadays). This adds several useful notes and many useful chords, but is still simple enough to find the notes and chords without having to think. I also play fully chromatic and regular diatonic dulcimers.
I have mountain dulcimers by Ron Ewing, Rod Matheson, Bear Meadow, McSpadden, Sweet-Water, and Jim Fox -- plus a cardboard one from Backyard Music. There are many other very fine builders, such as Blue Lion, Folkcraft, Jeremy Seeger, and others whose instruments I haven't played yet.
There's a second instrument, called the hammered dulcimer. If you're not familiar with it, see the photo. (Normally, it would be laying on a stand.) You hit the strings with pencil-sized drumsticks, so it's a bit like a piano or harpsichord, except that it's percussive. Mine has a 4-octave chromatic range and 95 strings.
Hammered dulcimers and mountain dulcimers are related like Lyndon Johnson and Magic Johnson.
I first got hooked on the sound of the hammered dulcimer in my teens, and after a decade of being a "groupie" and the token guitarist at dulcimer festivals, I finally bought one. They're fun to listen to and they're incredible fun to play, but recently I've been more focused on the mountain dulcimer.