What tool do you use to monitor your servers?
I'm looking for something to monitor intranet apps and internal web services, and provide logs of historical response times, uptime, alerts if the system becomes unavailable...
In short, I'm looking for something that's almost identical to Pingdom, but which can be run on an internal monitoring server so we don't have to expose our intranet pages and API endpoints to the outside world.
Open source, commercial, free - doesn't really matter. Just curious to know what's out there!