Recs.
Updated
Sentry is a log aggregation tool open sourced on GitHub and available as a SaaS at GetSentry.com.
Sentry was conceived in 2010 at Disqus and got the first paying customer in February 2012.
SpecsUpdate
Pros
Pro Pinpointing of errors (in your JS source file)
With Sentry, you won't have to get those meaningless and hard to figure out error messages with your minified JS files. All you need to do is provide Sentry with a source map and it'll decompress your JS file and pin point to which line is causing the error.
Pro Supports a number of different languages
The languages that Sentry supports includes Python, PHP, C#, Java, and Ruby. See the documentation for the full list.
Pro Consolidates similar errors and makes resolution easy
It's what Sentry calls [Rollups](https://docs.sentry.io/learn/rollups/]. All individual issues rolled-up can still be drilled down. Also two issues can be merged manually.
Cons
Con Setup instructions are poorly explained
The client keys page of the setup section has keys that have the public and private keys in them. This isn't explained on the page, so when integrating Sentry with another service, it's easy to mistakenly copy the private key when you wanted the public key.
Con Some old issues still not fixed
There are still some old issues, specifically speaking, with the Ruby Client that haven't been fixed yet.