Zabbix is the ultimate open source availability and performance monitoring solution. Zabbix offers advanced monitoring, alerting, and visualization features today which are missing in other monitoring systems, even some of the best commercial ones.
Below is a short list of features available in Zabbix:
- Audit logging
- Web-based interface
- Agent-less monitoring
SSS has been using Zabbix for quite a while and has a lot of experience in setting it up, configuring it so that you can monitor your availability and performance of your critical servers.