Reviewable

Reviewable is a code review tool for GitHub and GitHub Enterprise pull requests. Users sign in with their GitHub account, and the code remains stored on GitHub.

Reviewable tracks revisions of a pull request even when commits are rebased or amended, and shows the changes since each reviewer last looked. A file matrix records which revision of each file each reviewer has reviewed. Discussions stay open until each participant’s disposition resolves them. Review completion is defined by a customisable condition script that can, for example, require specific reviewers or approvals before merge.

Reviewable is a commercial service, free for public repositories, with paid subscriptions for private repositories.