Issues management is a script as heavy as a BBS system from the 80s. CI/CD totally depends on whatever you're building, so they can hardly include that in system requirements. Monitoring I don't use, so that shouldn't impact performance for me. Chat server is Mattermost, that's not a mandatory dependency I should hope? Anyway, wouldn't use it, so not applicable either. Container registry... a registry doesn't sound like much? But again, not applicable. I don't know why 4GB RAM is the absolute minimum for Gitlab.

All I want is a Github alternative: something which allows people to clone (be it http(s) or git smart something), do pull requests, have an issue tracker, view files online and show pretty markdown documents. I'm half inclined to go the usual route and write it myself, but I should first google around. Someone mentioned Gitea to me: that project claims to be lightweight so it might already fit the bill.