I tried some different products for network monitoring since the top dog Nagios is everything else but easy to maintain.
Tested products were:
- 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.
- 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.
- Homepage: http://community.zenoss.org/
Not really intuitive configuration. Supports Nagios plugins, offers own extension system (ZenPacks).