Well we are listed Nagios consultants...
Been using it since the Netsaint days before the name chance and re-design....

Currently we run it on Solaris boxes feeding a custom Cold Fusion provisioning application.
CF also dynamically builds the object files for automatic updates when networks change or are added on the fly...

Nagios can do much more than page one with up and down info about port/ping availibility.
You can monitor stuff like network, RAM, CPU, disk space utilization among many othere things.
There are many plugins and user contributions, to many to name specifically.

Ask not what nagios can do for you but define what needs you have and discover if nagios can help...

If you have a specific question, I'm happy to help you get going...!!