Sentry is an event logging platform primarily focused on capturing and aggregating exceptions.
If you're curious, you can read about how Sentry came to be on Leanstack.
It's all open source.
The hosted version of Sentry, that is, getsentry.com, is run by using the open source version of Sentry with a bit of proprietary code on top. That said, nearly every change that is needed for the hosted version to work is actually made upstream first, usually in the form of an extensible interface.
Want to learn more about the code? We host everything on GitHub.