GitLab, GitHub, BitBucket etc are not simply a GitServer, if that is all you want then there are better projects out there for that. hell basic ssh or http server can be used a gitserver with no front end at all or gitweb http://git-scm.com/docs/gitweb.html
GitLab, GitHub, BitBucket etc are project Management platforms that enable Bug Tracking, Documentation, Social networking all on top of and around basic git functions
just use git directly then without a gui server? or hell if you need a gui use upsource, that needs 8 gb ram however it is down you still could use everything else.
https://www.jetbrains.com/upsource/ (just repository browsing and code review not hosting, for hosting you need to create your bare repos yourself which is not hard)
GitLab, GitHub, BitBucket etc are project Management platforms that enable Bug Tracking, Documentation, Social networking all on top of and around basic git functions