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Open Source free powerful analytics tool.
Graylog2 enables you to unleash the power that lays inside your logs. Use it to run analytics, alerting, monitoring and powerful searches over your whole log base. Need to debug a failing request? Just run a quick filter search to find it and see what errors it produced. Want to see all messages a certain API consumer is consuming in real time? Create streams for every consumer and have them always only one click away.
Used by both startups and major corporations all over the world.

Start-ups using:

Graylog2