Nagios is an open source computer system and network monitoring application. It watches hosts and services, alerting users when things go wrong and again when they get better. 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.
Centreon is a network, system, applicative supervision and monitoring tool, it is based upon Nagios. Centreon provides a new frontend and new functionnalities to Nagios.