Logstash - Centralized log storage, indexing, and searching
Logstash is a tool for managing events and logs. You can use it to collect logs, parse them, and store them for later use. Logstash comes with a web interface for searching and drilling into all of your logs.
You can ship logs from any source, parse them, get the right timestamp, index them, and search them. You can query for more precise things like, 404 http errors, nagios critical alerts in hard state, or mail server faults - all without accidentally finding logs with the word '404' or 'critical' in the wrong place.
Logstash could scale horizontally. It runs as standalone service or in client-server mode. It also understands AMQP protocol and recommends RabbitMQ as message broker.