cPanel - With its first-class support and rich feature set, cPanel & WHM has been the web hosting industry's most reliable, intuitive control panel since 1997.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Webmin - Webmin is a web-based interface for system administration for Unix.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Vesta Control Panel - – What I love about Vesta is that it's fast and easy to use
Prometheus - An open-source systems monitoring and alerting toolkit.