The author is Gregg Miner, and Gregg has an extensive library of harp guitar music. A long time ago I met Gregg when one of my friends Brad Hoyt (a keyboard and harp guitarist as well) hosted a harp guitar convention here in Indianapolis, and I got recruited to help. Gregg and the rest of the artists that were there were extremely approachable, and most of the crowd were musicians (some pretty famous ones, too) checking out one of the more interesting variations of the guitar... and what you could do with one. Fun times.
I'm probably preaching to the choir in a story about guitars, but if you're looking for some good 12-string music, Leo Kottke's 6 and 12 String Guitar is a good start.
If you haven't heard (or seen) Michael Hedges play a harp guitar, there's some background and links to videos here:
You only have to put your finger somewhere in between two frets to get a particular note, so you can play more than the tiny handful of chords that can be played on something like a violin.
There are non-fretted guitars but they are rare, and I think early banjos were not fretted.
There are those who say it isn't a chord until you have 3 notes. I'm going to skip the complex music theory behind the arguments (I haven't studied them enough to understand much less form an opinion).
Of course in most music contexts there is more than one instrument playing and so the others can fill in the missing note making a full chord. Only a "one-man-band" really feels the loss.
What I love about links like this is that we see information being shared just for the love of it. This person has done a lot of work simply to share knowledge with the world about something they are passionate about. This is what great about the internet and is easily lost amongst all the commercial content.
If you haven't heard (or seen) Michael Hedges play a harp guitar, there's some background and links to videos here:
https://michaelhedges.com/michael-hedges-the-harp-guitar/
If you haven't heard them yet, you're in for a wild ride: https://www.youtube.com/@AnginePoitrine
I see your added frets, and raise "add frets on the fly using Lego":
https://www.youtube.com/watch?v=rPCEImSfCwc
Really? I highly recommend Flying Microtonal Banana.
You only have to put your finger somewhere in between two frets to get a particular note, so you can play more than the tiny handful of chords that can be played on something like a violin.
There are non-fretted guitars but they are rare, and I think early banjos were not fretted.
What do you think double-stops are?
Of course in most music contexts there is more than one instrument playing and so the others can fill in the missing note making a full chord. Only a "one-man-band" really feels the loss.
That's E, G♯, B, D, F
* https://www.delta-harp.com/
* https://www.youtube.com/watch?v=IdUztFVwi3I