If you are able to do this kind of infrastructure work, there are literally multiple git managers which are free (libre and gratis!) and just as powerful for developers. My employer, OSUOSL, deploys an internal gitolite and we do just fine.
Gitolite only does a tiny fraction of what github offers. The two really aren't directly comparable. Gitolite is purely a code hosting system, github allows you to collaborate, view code with an awesome viewer, make comments and much more.
