http://phabricator.org/ covers precisely that - code reviews and discussions around commits. The recommended installation includes Arcanist command line tool, which modifies Git commit template to include a URL of the Phabricator code review, test plan, and reviewers' names.
Hmmmm I'm not sure it does. The problem (I have experienced) with Phabricator is that it only operates on the diff you upload, so it can lack context of the project as a whole.
