The Dude network monitor is a new application by MikroTik which can dramatically improve the way you manage your network environment. It will automatically scan all devices within specified subnets, draw and layout a map of your networks, monitor services of your devices and alert you in case some service has problems. See MikroTik Forum - The Dude download is dead. for download links.
Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and Grids.