We've been using Rollbar for a number of apps over the past few months and have really been liking how it fit into our infrastructure. Brian has been great about responding to bugs and suggestions. Keep up the great work!
Don't forget about about Sentry (https://getsentry.com/welcome/) which is also open source (https://github.com/getsentry/sentry) and can be self hosted. I've only used it with Python, but it has so far been infinitely better than the alternatives I've tried (probably because it's written in python). Integration with Flask is a 3-minute affair.
If any Airbrake/Exceptional users are looking for an alternative, check out Rollbar (https://rollbar.com). Here's a write-up we did on how we're different from Airbrake: https://rollbar.com/vs/airbrake/