Nagios (formerly Netsaint) is a daemon written in C that is designed
to monitor networked hosts and services. It has the ability to notify
contacts (via email, pager or other methods) when problems arise and
are resolved. Host and service checks are performed by external
"plugins", making it easy to write custom checks in your language of
choice. Several CGIs are included in order to allow you to view the
current and historical status via a Web browser, and a WAP interface
is also provided to allow you to acknowlege problems and disable
notifications from an internet-ready cellphone.