* [Healthchecks](https://healthchecks.io/) - Monitoring for cron jobs, background services and scheduled tasks.
* [Icinga](https://www.icinga.org/) - Nagios fork that has since lapped nagios several times. Comes with the possibility of clustered monitoring - ([Source Code](https://github.com/Icinga)) - `GPLv2`
* [Icinga](https://www.icinga.com/) - Nagios fork that has since lapped nagios several times. Comes with the possibility of clustered monitoring - ([Source Code](https://github.com/Icinga)) - `GPLv2`
* [LibreNMS](http://www.librenms.org) - Fully featured network monitoring system that provides a wealth of features and device support.
* [Monit](http://mmonit.com/monit/#home) - Small utility for managing and monitoring Unix systems.