Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
AlienVault OSSIM - Alienvault integrates and correlates many popular network and security monitoring tools in one...
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.
Splunk - Splunk's operational intelligence platform helps unearth intelligent insights from machine data.
Prometheus - An open-source systems monitoring and alerting toolkit.
SIEMonster - A very powerful and well documented open source SIEM with options to purchase support packages.