there's https://forgefed.org/ defined by the creators of forgejo. there is no complete implementation of the spec. from the last forgejo changelog, the "star" action has been completely federated. federated PRs and issues are a long way away.

https://tangled.sh is the other contender in this space that I know of. uses atproto (same as bluesky) under the hood.

fundamentally activitypub is insufficient to define these kind of networks. you'd need to have some sort of object-capability representation. the creators of forgefed are also moving in this direction: https://codeberg.org/Playwright/playwright