Zabbix is an enterprise-class open source distributed monitoring
solution.

Zabbix is software that monitors numerous parameters of a network and
the health and integrity of servers. Zabbix uses a flexible
notification mechanism that allows users to configure e-mail based
alerts for virtually any event. This allows a fast reaction to server
problems. Zabbix offers excellent reporting and data visualisation
features based on the stored data. This makes Zabbix ideal for
capacity planning.

WWW: http://www.zabbix.com/
