Working demo of 3point body IK in javascript. Open with firefox (or recent versions of chromium, i think they have support now)
https://avatars.exokit.org/ 

hit the "enter xr" button and put on your headset. You can switch avatars on the left menu (in desktop). The author somehow parses unitypackages and tries to find vrchat-compatible armatures.

A little bit janky, but still impressive for a proof of concept. I didn't try the "multiplayer" button but I think if you do it sets up a little webrtc room.