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.
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.
Review Assistant is a code review plugin for Visual Studio. The code review tool allows creating review requests and responding to them without leaving Visual Studio. Review Assistant supports TFS, Subversion, Git, Mercurial, and Perforce.