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.
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.
Heka - heka - Data collection and processing made easy.
Prometheus - An open-source systems monitoring and alerting toolkit.
logstash - logstash is a tool for managing events and logs.
Gravwell - Gravwell is an all-you-can-ingest data fusion analytics platform that enables complete context and root cause analytics for security and business data.