log.io - Real-time log monitoring in your browser
Fluentd - Fluentd is a cross platform open source data collection solution originally developed at Treasure Data.
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.
Splunk - Splunk's operational intelligence platform helps unearth intelligent insights from machine data.
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.
Graylog - Graylog is an open source log management platform for collecting, indexing, and analyzing both structured and unstructured data.