correction/update.

I kept digging for information on that weird 5-course instrument, and I found a much more complete (and likely) origin, from the Scandinavians themselves:

https://silkwoodmusic.wordpress.com/2010/03/25/the-nordic-mandola-its-not-a-banjo/

Notes:

1. The part about calling it a cittern because the word was available: true enough.
2. Only being able to get one used or custom-built: still true.
3. Wait. Quarter-tone frets? What?
4. Single-string capo pegs that screw into the fingerboard?!
5. I'm 99% sure theorbed wasn't a word before this guy typed it, but what he means is having a second set of strings ending beyond the first set, thus with lower pitch, usually as drone strings. There's, uh, some variety in how this is done in a theorbo.

I don't really want to pay a few thousand dollars for a custom instrument; I expect violins will keep me busy for a long time. I've been watching people play these things, thinking about what I find appealing in them, and it's really that they look much easier to play. In the original video I saw, if you look at Ale Carr's left hand, he rarely has more than two fingers holding strings down, because the instrument is tuned to something close to an "open tuning," where strumming the strings without any fingers down (the "open" bit), plays something closer to a pleasant-sounding chord. Most ordinary tunings, for most instruments, are not chord-friendly, for various historical and music-theory reasons.

Then I started thinking that I have quite a nice guitar here, and partial capos, which don't cover all 6 strings, are totally a thing. This guy takes it to what is probably an extreme, but I'm pretty sure I can have a lot of the fun of these weird Nordic instruments, using just my guitar and some toys.