Phabricator[0] is a more mature alternative if anyone is interested in an open source and free substitute for GitHub. I think the only thing GitLab might have over Phabricator is a familiar GitHub like UI. Phabricator was an internal Facebook project that was open sourced. It's actually far more than just a substitute for GitHub. It has a much better system for managing issues, and better code review tools as well as other powerful features. My favorite feature is the herald system[1].
[0] http://phabricator.org/
[1] https://secure.phabricator.com/book/phabricator/article/hera...