Nagios

Nagios is one of the original open-source IT infrastructure monitoring platforms, providing comprehensive monitoring of hosts, services, and network devices. Despite being one of the oldest monitoring tools, Nagios remains widely deployed and maintains an active community. Nagios Core provides the foundation with host and service monitoring, event handling, and alerting. Thousands of community-developed plugins extend Nagios to monitor virtually any technology. Nagios XI is the commercial version, adding a web interface, configuration wizards, capacity planning, and advanced reporting. Nagios established many of the monitoring patterns and concepts that newer tools have built upon, including check-based monitoring, escalation policies, and passive check submission. Its architecture supports distributed monitoring across multiple locations and network segments.