we work on a lot of projects hosted on GitHub. While GitHub's PR model is simple to use, it creates a workflow where the typical output is a large pull request. These PRs often address many dimensions of a feature or fix all at once, and are very unwieldy to review.
We longed for power tools like the internal code review apps at Google (Critique/Gerrit) and Facebook (Phabricator). We wanted our tools to encourage meaningful commits as checkpoints for feedback. We wanted a workflow encouraging more incremental output that's easier on reviewers.