Yeah, sadly IIRC a mixture of quaternion trouble (weak maths skills) plus an ME flareup put this one on hold indefinitely. I’ve dug out what I believe was the last version I have. I couldn’t attach it here for some reason (maybe file size). If you PM me an email, I’ll shoot it over that way. Not sure what state it’s in, and can’t speak to code quality/idiomatic approaches, but it should at least give you a partially working implementation to reference. If you understand how to use quaternions in Panda, you can probably fix what’s there pretty quickly. I think I was also looking at integrating it into a “fake” looping one-frame animation (so you could blend IK with existing animations). There may or may not be code for that in there, but if you spot any, that’s what it’s for 
. Unfortunately the model I used for testing wasn’t archived with the files, but I pulled what could very well be the same model from another source. Fingers crossed that’ll let you get the test scripts running without too much fuss, so you can see where I left things.
I still remember a fair bit about the original FABRIK papers I read (there are more than one, and I remember some giving nuggets of info not present in others), so feel free to PM me if you have questions, and I’ll try my best to answer them. Good luck.