Nagios is a widely-used open-source monitoring system designed to oversee the health and performance of IT infrastructure. It helps organizations proactively identify and resolve issues by offering monitoring capabilities for servers, network devices, applications, and services. Nagios provides robust alerting and reporting features, allowing IT teams to respond to incidents swiftly and maintain optimal system performance. Its flexibility and extendibility are bolstered by a variety of plugins and integrations, catering to diverse monitoring needs.