Riemann is an open source server that aggregates and relays events in real time. Written in Clojure, and based on Netty, it is capable of handling thousands of concurrent connections per node. Riemann uses a simple Protobuf protocol for events, which allows it to aggregate everything from CPU and memory use to orders placed to error rates. It forwards to systems like Graphite, triggers email alerts, and provides a dashboard for monitoring these metrics. Riemann is an important part of the movement towards handling data as generic streams of events in real-time, as opposed to using specialized systems for different types of data.