GitHaven was created out of the need to be installed behind a firewall inside a corporate intranet or for personal use at home. GitHaven is packaged as a Debian package so it is extremely easy to install and keep updated.
Besides being open source the one feature that GitHaven has the GitHub doesn't is the ability to add top level tabs. So if you want a tab called "Wiki" and it points to your wikipedia entry the Admin can add it. This allows you to easily incorporate with other tools (mostly bugtrackers which are often Jira, Bugzilla or other)
While I still use it for my own personal use I am no longer permitted to develop GitHaven so it has been released under the AGPL in the hope that it can be useful for others.