PushRadar is a realtime notifications API using two simple lines of code to publish and subscribe to notifications.
If you use Google Analytics, you'll benefit from StatsGlitch. Statistically significant, custom & real-time alerts will cover all your business needs.
Weekly overview report will make you happy and confident, that everything is OK.
You're already using mixpanel to track events, but some events deserve special attention. e.g. you track signups. But does a John Doe signup event equals a Mark Zuckerberg signup event?
With pingpoint, you can alert anyone in your organization when these super important events happen, so they can act instantly.