Phabricator is an open source software development platform written in PHP. Its applications include the Differential code review tool, Diffusion repository browser, Herald change monitoring tool, Maniphest bug tracker, Phriction wiki, Conpherence chat, and Conduit API. You can download and install it on your own hardware for free, or launch a hosted instance that gives access to automatic updates, maintenance, and support.
It's fast, scales well, and is best suited for large projects with multiple repositories. While the UI has been criticized for being unintuitive, it is customizable and can be tailored to your specific team.