Isn't radicle quite similar? https://radicle.xyz/

You are correct. Someone posted about Radicle here a couple days ago[1] and went down that rabbit hole. The user docs say that their p2p network draws inspiration for Secure Scuttlebutt's gossip protocol.

I'm not 100% sold on federation / activitypub in its current state. I think p2p is far more interesting. With Radicle, you don't have to run a server (which, if Mastodon is anything to go by, is a lot of overhead). So anyone can try it! Radicle is ready to use right now.

[1] https://news.ycombinator.com/item?id=44874945