Forum Moderators: phranque
Can't get much cheaper than an open source project -- Nagios [nagios.org]
System Requirements
The only requirement of running Nagios is a machine running Linux (or UNIX variant) and a C compiler. You will probably also want to have TCP/IP configured, as most service checks will be performed over the network.
You are not required to use the CGIs included with Nagios. However, if you do decide to use them, you will need to have the following software installed...
A web server (preferrably Apache)
Thomas Boutell's gd library version 1.6.3 or higher (required by the statusmap and trends CGIs)