xymon

Xymon (previously called Hobbit) is a network- and applications- monitoring system designed for use in large-scale networks. But it will also work just fine on a small network with just a few nodes. It is low-overhead and high-performance, with an easy to use web front-end. Network services are monitored remotely. Machine health and statistics are monitored through a locally installed client package (xymon-client). Additional (remote as well as local) checks are available in the package hobbit-plugins. Alerts can trigger when monitoring detects a problem, resulting in e-mails or calls to your pager or mobile phone. Xymon has a great deal of inspiration from the non-free Big Brother package, but does not include any Big Brother code.