Gitorious is an open source Git server! Allows you to host your own Git repository :) http://www.gitorious.org
Side note: check this plugin out:
Git p4 allows the cloning of a perforce repository into a git one and back.
Git wiki: https://git.wiki.kernel.org/index.php/GitP4
Git docs: http://git-scm.com/docs/git-p4
There is also a perforce product called git fusion which seems cool for enterprise: http://www.perforce.com/git-fusion