I've been following the software forge federation some time ago, and didn't feel to pick up even when it was discusssed initially. It is a neat idea on high-level, though it requires forges to implement it, which has a risk of not picking up (just look at how much iterations of social media federation protocols was there, until ActivityPub arose).
On the other hand, all of the forges are based on a distributed technology out of the box: git. Most of the "modern days" comforts there are, are just built on top, and there are different ways to approach it.
As an example, you can send patches directly to the author in email. Is heavily implemented and suggested by https://sr.ht/ (1) — a software forge, which focuses on building a federated workflow by using email for communication (which is federated by design). This way, you can create "Pull Requests" without having account on the forge — all you need to do is just submit a patch. Author is very vocal about supporting it (2), and provides quite useful guides to learn (3), (4)
Generally, I'd say that e-mail is the only federative implementation you can get so far :)