We also use it. Replaces Zenoss in my toolbox. Much wider scope than Nagios (has reporting etc built in.) Unlike Zenoss it is real Open Source, - you get ever

We also use it. Replaces Zenoss in my toolbox. Much wider scope than Nagios (has reporting etc built in.) Unlike Zenoss it is real Open Source, - you get everything in the default download, the only thing you pay for is support etc (and while I haven't needed it yet I'll happily argue to pay for support the day we need it.)