Zenoss is a nice NMS. The main Zenoss advantage is the flexibility offered by its modular (ie."plugin") system called zenpacks.
At this Address there are plenty of zenpacks: http://community.zenoss.org/community/zenpacks.
You’ll be tempted to get as many as you wish, then install them from the WEB-GUI.
Unfortunately the WEB-GUI doesn’t always succeed on showing you what is really happening, so installing zenpacks from CLI sometimes may offer you more clues.
To install zenpacks through bash, I do:
chown zenoss:zenoss /path/to/zenpack.egg
chmod 777 /path/to/zenpack.egg
/usr/local/zenoss/zenoss/bin/zenpack --install /path/to/zenpack.egg
And make sure you read the output!
To restart Zenoss.
Usually everything will be fine, except for the occasional HP Procurve Zencack, that requires you to manually create the /Devices/Network/Switch/HP class and the /Events/Net/traps event.