Phabricator is a collection of open source web applications that help software companies build better software.
Effective June 1, 2021: Phabricator is no longer actively maintained.https://admin.phacility.com/phame/post/view/11/phacility_is_winding_down_operations/
Review Board is a web-based collaborative code review tool, available as free software under the MIT License. Review Board can be installed on any server running Apache or lighttpd and is free for both personal and commercial use.
Gerrit simplifies Git based project maintainership by permitting any authorized user to submit changes to the master Git repository, rather than requiring all approved changes to be merged in by hand by the project maintainer.
MergeBoard is the first code review tool to display code changes in a smart way. Its unique features help developers spend less time on code reviews and catch more bugs.