I tried some different products for network monitoring since the top dog Nagios is everything else but easy to maintain.

Tested products were:

• OpenNMS
• Zenoss Core
• Pandora FMS

OpenNMS

• Homepage: http://www.opennms.org/

Configurable by XML files, so suffers the same problem as Nagios – you need something to configure it comfortably or spend time writing the config yourself. Compatible to Nagios plugins.

Pandora FMS

• Homepage: http://www.pandorafms.org/

Really great interface. Supports Nagios plugins. Easy addition of own plugins. For me, this one had the best feature set.

Zenoss Core

• Homepage: http://community.zenoss.org/

Not really intuitive configuration. Supports Nagios plugins, offers own extension system (ZenPacks).