Self-hosting with open source code:

- SourceHut: https://sr.ht/~sircmpwn/sourcehut/

- Forgejo (used by Codeberg, etc.): https://forgejo.org/

SourceHut never really clicked for me. It doesn't give me anything useful that I don't already have in a bare git repo through a ssh.

Forgejo, on the other hand, is a drop-in replacement for GitHub.