With Servo we use <a href="https://reviewable.io/" rel="nofollow">https://reviewable.io/</a> on github.<p>We don't enforce its use. If a newcomer makes a pull request, we'll just use the GH review interface. In general simple PRs go through the GH review interface, regardless of who they're from. We break out Reviewable when a PR actually <i>needs</i> it (this is usually the choice of the reviewer).<p>This means that Servo continues to have a lower bar to contribution, without hampering maintainers on PRs that need more than GHs set of review features.<p>This has worked out well for us.