Nagios released another point update this past week bringing it to 3.0.6. The changelog reports only a few minor fixes and additions. I noticed the available update during my weekly server updates time. Remember that on Linux systems you must restart the service (daemon) to run the new version (command: service nagios restart).
Nagios is an opensource service/host monitor that allows the everyday sysadmin to keep tabs on all of the crucial network services and hosts. You can setup all kinds of checks and then be notified should any crucial hosts or services are down.
Setting up your own Nagios installation can be difficult, but many tutorials exist online. If you would like assistance designing and deploying your own Nagios installation please contact me.