Review Board vs Upsource: What are the differences?
Developers describe Review Board as "Stress-free code review for teams of all sizes". Review Board is an open source, web-based code and document review tool built to help companies, open source projects, and other organizations keep their quality high and their bug count low. On the other hand, Upsource is detailed as "Self-hosted Git, Mercurial, Subversion and Perforce repository browser and code review tool". Upsource summarizes recent changes in your repository, showing commit messages, authors, quick diffs, links to detailed diff views and associated code reviews. A commit graph helps visualize the history of commits, branches and merges in your repository.
Review Board can be classified as a tool in the "Code Review" category, while Upsource is grouped under "Code Collaboration & Version Control".
Review Board is an open source tool with 1.19K GitHub stars and 359 GitHub forks. Here's a link to Review Board's open source repository on GitHub.