Not sure if it's a precursor, but this came across my radar: https://gitlab.futo.org/videostreaming/grayjay
Based on polycentric https://youtu.be/xYL96hb_p78?feature=shared
The system looks A LOT like nostr, but it seems to be developed internally as opposed to nostr that's developed in the open by any and everyone.
I may be wrong about that though, I may just be in the nostr bubble and not in the polycentric community (although I didn't find any polycentric community).