I just checked git-appraise and while it looks rather mature, it uses (as far as I can see by now) an approach which is not that nice if you have multiple public remotes. Also, as far as I can see, each submitter must be able to push to that remote - please correct me if I'm wrong.

We have a different approach for this, which is more powerful (talking about how the data is stored).

Of course, our tool is not mature yet. Maybe gitlab can learn from what we've researched...