Software development has been surprisingly resistant to "management by numbers". Stay away from vanity metrics and rate pull requests yourself using our smart sampling algorithms.
Heartbeat is currently under development and only available in private beta.
It works via a Chrome extension that overlays any GitHub pull request with a private feedback form that asks the question "Would you like to see more or less pull requests like this one?". This NPS-like question is designed to both focus your thinking on the behaviour you should reward (or if necessary, punish) in your team and stay open ended enough to be applicable to every development team.
If you haven't rated enough in a time period we'll nudge you to do so using smart sampling algorithms to get effective coverage. We then generate weekly, monthly, and yearly reports sliced by codebase and contributor so you can track progress over time.