Zabbix

Zabbix is a great Network Management System. It has all what I want:
- SNMP v1, v2, v3
- own agent collect information from Linux, Windows ...
- great web interface written in PHP
- generate alert, graphs, SLA
- well documented
- very stable !!!

New in v 1.6:
- Zabbix proxy = it's a gateway to forward results from agent to master server, great for distributed monitoring
- Nice graphs = 2D and 3D
- Support IPMI
- Optimized SQL for better speed
- and many more.

I am using Zabbix for about 2 years a I can say its perfect. I think it's a best monitoring system I ever seen.

I really like Zabbix, because:
- very advanced monitoring capabilities
- it combines graph-plotting(like cacti) and status monitoring (like nagios)
- it supports distributed monitoring
- very easy to enhance
- it support monitoring by SNMP, website-monitoring, IPMI and using a zabbix-agent(best)
- in the last months of usage (300 hosts) i never got a problem with it
- it´s very reliable
...

What i miss:
- jmx Monitoring for java-applications
(currently in development)
- automated reporting (create availability reports and send them to users)