I mirror the code I rely on and like, except for things that are just too large my servers get upset. Most of the code here is used by my own applications. I vendor most of my dependencies for this reason as well, but for other apps I just use this works. Speaking of which, I need to mirror more things!
https://git.vaughnnugent.com/cgit/
Funny enough I think, git itself has mostly migrated to GitHub. Can't speak for development, but all the documentation links back to GitHub.