Icinga
Icinga monitors availability and performance, gives you simple access to relevant data and raises alerts to keep you in the loop.
- Snippet from Wikipedia: Icinga
Icinga is an open-source computer system and network monitoring application. It was created as a fork of the Nagios system monitoring application in 2009 in an attempt to improve on Nagios' development process. The first stable version, 1.0, was released in December 2009. In 2010 it was described as offering better database connectors, web interface, and API than Nagios.
In 2012, development of a new core component was started and released in 2014 as Icinga 2 to allow for profound architectural changes compared to the Nagios core.