Graylog2 is an open source syslog implementation that stores your logs in MongoDB. It consists of a server written in Java that accepts your syslog messages via TCP or UDP and stores it in the database. The second part is a Ruby on Rails web interface that allows you to view the log messages. It also implements GELF. The Graylog Extended Log Format is a simple JSON string that allows you to send long and structured syslog messages and very useful for customized application log monitoring.