https://github.com/getsentry/sentry or hosted https://getsentry.com/
For anyone looking to implement something like Haystack, definitely give Rollbar a look -- you'll find most of these capabilities there (and much more). And if any of the Haystack or GitHub devs have had a chance to play around with both, I'd be really interested to hear any feedback; drop me a line (email in profile).
Our goal is to make dealing with errors so awesome that you'll want to get more of them. :)
For example, we can show you all of your logging statements that happened before and after the error on the same web request.
-Founder of Stackify
EDIT: or actually, since this is a count, might as well go straight for the poisson distribution or negative binomial -- same idea.
Tools like these become pretty invaluable when releasing code into the wild, and aside from lifecycle benefits like greatly reducing the cost of the maintenance phase, an error tracker can also alert and hand the data needed to fix the bug right to the person who can, greatly increasing dev sanity (no more relying on support ticket ping pong, and removes the onus on the end user to report the bug). Also, surfacing the attack vectors and the frequency of which adversaries attack code exposed to the web is rather eye opening.
if I had to take a stab at it, I'd say a good place to start is some ELK platform. Seems like it has almost all of the right components to build something like this. Just curious if they have their apps directly feeding exceptions, or if they are slurping logs.