[yakiv]

One possible backup would be Bitbucket (https://bitbucket.orghttps://bitbucket.org/).

(I'm not affiliated Bitbucket in any way. I don't profit from them doing well, aside from them sticking around to keep providing free hosting for me.)

[ajross]

Another possible backup is any host on the internet. Seriously, dump it into a static file directory on any old web server or run a trivial git server. Send deltas with patch files. It's not even harder than github is, just uglier.

[bitcartel]

If you want to use your own servers, Atlassian (who own Bitbucket) recently released Stash, a competitor to Github Enterprise. Pricing is very good and if you have a commercial license, you also get the source code.

[lflux]

I've evaluated Stash a couple times, and I feel that Gitlab still has it beat.