* [Alerta](https://github.com/guardian/alerta) - Distributed, scaleable and flexible monitoring system.
* [Alerta](https://github.com/guardian/alerta) - Distributed, scaleable and flexible monitoring system.
* [BandwidthD](http://bandwidthd.sourceforge.net/) - BandwidthD tracks usage of TCP/IP network subnets and builds html files with graphs to display utilization.
* [Cacti](http://www.cacti.net) - Web-based network monitoring and graphing tool.
* [Cabot](http://cabotapp.com/) - Monitoring and alerts, similar to PagerDuty.
* [check_mk](http://mathias-kettner.com/check_mk.html) - Collection of extensions for Nagios.