Formerly known as Netsaint, Nagios is a recursive acronym to Nagios Ain’t Gonna Insist on Sainthood. Nagios is a well known, industry standard IT network traffic monitoring application. The user needs to specify the hosts and services to be monitored. Nagios reports when things go from good to bad or when things improve on the wire. This IT security audit tool acts as an intrusion detection system by providing alerts on any form of security breach. It enables sharing of reports among the stakeholders of the organization.
You can download this tool here.