Only really self-hosting. But many would consider the admin of that to push it away from the definition of "decent".
You can host a git repository on any server. The Linux kernel is not developed on github, is it?
Github is far from just a git repository. It's a ticket tracking system, a discussion system, a release binaries host, a CI/CD component and a pastebin. The linux kernel has no CI/CD, no binaries, it doesn't even have a centralized server (only a copy of Linus' tree) and does everything through mailing lists.
Well, if you want all of those things in one place, then that means github, practically by definition. But the example of the kernel shows that open source can carry on, on a massive scale, with no need for that.
GitLab also has all of these features, and it had many of them before GitHub, like built-in CI/CD. But for some reason I'm being downvoted for suggesting it on HN, curious why.