Went down the rabbit hole the other day, looking and unusual instruments.
First up, the Gittler Guitar, no fret board, no wood:
The old and beautiful wheelharp:
The diddley bow has a long, interesting history. I like this electric version.
The microtonal guitar. If you want to see him play the “completely messed up” one, skip to about 3:40.
Finally, a little outsider art: the Anarchistra: