Nagios Open Source network monitoring software - The Standard In ITM
Nagios network monitoring software is a powerful, enterprise-class host, server, application, and network monitoring tools. Designed to be fast, flexible, and rock-solid stable. Nagios runs on *NIX hosts and can monitor Windows, Linux/Unix/BSD, Netware, and network devices.
An easy alternative for monitoring network infrastructure services. Focused on monitoring without requiring server changes or even special requirements on the monitoring machine. Can monitor remote systems via SSH or other communication channels. Intended to be extremely easy to use especially in smaller and medium sized network environments.