Check_MK is a free and open source IT monitoring tool for Linux like Operating Systems. Check_MK replaces the standard Nagios GUI & way the systems are monitored on Nagios, it provides graphical administration of monitoring & boosts other features like auto detection of configurations in a monitored system, specials checks in addition to Nagios checks, SNMP based agentless monitoring, filtering, viewing & alerting for log files & event data.