Nagios of course, nothing more to say.

Nagios is ok, but Shinken as a Python based Nagios replacement realy rocks

It definietly rocks..been using it for several companies that I've moved with.

Shinken, as it evolves quite fast and has had innovative features in 2011.

I only recently heard of nagios. (Our network is under 20 workstations with only a few servers) I'll have to look into the others listed in this thread.

Nagios is very good tool !

Shinken FTW

I miss isyVmon (www.isyVmon.com) in the list

ONLY
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nagios is it for me.

...and the winner should be Nagios!!

I don't see http://portal.monitis.com/ on the list.

I have used OpenNMS, it is quite simple for monitor network device
Nagios is difficult to use for beginner. for example to view cisco switch port traffic info, you have do lot of settings

Very scalable.
Very flexible.
Distributed, load balancing possible without much brainache.
n-tier layer splitting possible.
Extremely cost effective if you like the benefits of the XI version.
HUGE community support. Somebody somewhere will have already done what you are trying to do!

Enterprise proven and ready

I vote for Shinken.

It has a painless complete distributed and HA architecture. It supports standard Nagios(R) Livestatus and plugins. It has the innovation and vision that has been sorely been lacking in the Nagios world, without sacrificing the knowledge and plugins.

A solid frontend only brings you so far, but for major deployments, you need to have the mechanics under the hood to drive it.

Zabbix is the close second with solid scalability, features, maturity and large installation user base.

Opsview(nagios core) has a good understanding in providing concise interfaces.

Monolith-systems is where its at for commercial big dollar systems.

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