At my last job I ran a GitLab instance on a tiny AWS server and ran workers on old desktop PCs in the corner of the office.

It's pretty nice if you don't mind it being some of the heaviest software you've ever seen.

I also tried gitea, but uninstalled it when I encountered nonsense restrictions with the rationale "that's how GitHub does it". It was okay, pretty lightweight, but locking out features purely because "that's what GitHub does" was just utterly unacceptable to me.