freebsd-ports/net/nagios/pkg-descr

Nagios is a host and service monitor designed to inform you of network
problems before your clients, end-users or managers do. It has been
designed to run under the Linux operating system, but works fine under
most *NIX variants as well. The monitoring daemon runs intermittent
checks on hosts and services you specify using external "plugins"
which return status information to Nagios. When problems are
encountered, the daemon can send notifications out to administrative
contacts in a variety of different ways (email, instant message, SMS,
etc.). Current status information, historical logs, and reports can
all be accessed via a web browser. 

WWW: http://www.nagios.org/