Bunch of interesting instruments there, actually… Sounds pretty awesome!
Not quite sure what that is, exactly, but it looks a bit familiar… There are loads of different variants of these instruments, especially from the medieval period, before things started to converge towards the modern violin family instruments.
This one kind of looks like a crossbreed of cello, viola da gamba, and a pochette violin. As for the tied frets (likely gut - at least that’s what was used traditionally), those are typical for viola da gamba, and many other renaissance instruments, and can actually be used on more modern cello variants as well, in particular, the violoncello piccolo, when playing baroque repertoire. For example: