Munin is an open source, web-based network and system monitoring application. It helps users to monitor their servers, networks, and other services in a centralized location. It provides real-time monitoring of services, server performance metrics, and more. It is designed to be easy to use and configure, with a simple and flexible architecture. It can be used to monitor any number of servers and devices, including routers, switches, firewalls, and load balancers. Munin provides detailed performance data that can be used to identify potential issues and performance bottlenecks. It also provides alerting capabilities to notify users of any changes in performance. Munin is available for both Linux and Windows platforms.
Much faster to set up than any of the free tools, really worth the money.