* Argus is a system and network monitoring application.
* It will monitor nearly anything you ask it to monitor (TCP + UDP
  applications, IP connectivity, SNMP OIDS, Programs, Databases,
  etc).
* It presents a nice clean, easy to view web interface that will keep both the
  managers happy (Red Bad. Green Good.) and the techs happy ("Ah! that's what
  the problem is").
* It can send alerts numerous ways (such as via pager) and can automatically
  escalate if someone falls asleep.

WWW: http://argus.tcp4me.com/