Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and grids. It is based on a hierarchical design targeted at federations of clusters. Ganglia is currently in use on over 500 clusters around the world and has scaled to handle clusters with 2000 nodes.
nexB OpenAssets is a tool for inventorying, managing, and monitoring applications, software, hardware, networks, and generally any IT asset. It is designed so that system administrators, IT, and finance can determine what they have, how it is configured, what it is used for, and how much it is being used, so that informed decisions can be made. It complements existing network management software, integrates with a growing number of protocols and tools, and features no-agent discovery and inventory, configuration management including dependencies and correlation, monitoring, and reporting. It makes extensive and innovative use of XML, Xpath, and Xquery.
PortSensor is a powerful Windows/Unix server monitoring tool with Linux/Mac/Windows clients. Sensors can be created to monitor nearly any TCP/UDP service, such as: HTTP, FTP, POP3, SMTP, MySQL, and DNS. Custom sensors can be created to monitor your other critical server metrics, such as processor loads, mail queue loads, disk space usage, and log activity.