Zabbix - distributed monitoring solution
Zabbix is an enterprise-class open source distributed monitoring solution. It is highly scaleable, capable of monitoring more than 100,000 devices and servers. A Zabbix agent can also be installed on UNIX and Windows hosts to monitor statistics such as CPU load, network utilization, disk space, etc. It also supports agentless monitoring via SNMP, TCP and ICMP.
It monitors performance in real time and alers users via mail, SMS, Jabber (XMPP) clients. It supports variety of database including Oracle, MySQL, PostgreSQL, SQLite. Web based interface to visualize the data and generate reports and stats.