Nagios provides features such as alerting, event handling and reporting.The Nagios Core is the heart of the application that contains the core monitoring engine and a basic web UI. On top of the Nagios Core, you are able to implement plugins that will allow you to monitor services, applications, and metrics, a chosen frontend as well as add-ons for data visualisation, graphs, load distribution, and MySQL database support, amongst others.
Tip: If you want to try out Nagios without needing to install and configure it from scratch, download Nagios XI and enable the free version.
Note: The free version of Nagios XI is ideal for smaller environments and will monitor up to seven nodes.
Nagios XI is the pre-configured enterprise class version built upon Nagios Core and is backed by a commercial company that offers support and additional features such as more plugins and advanced reporting.