Apache Storm : Distributed and fault-tolerant realtime computation

http://storm.incubator.apache.org/
http://storm.incubator.apache.org/documentation/Tutorial.html
http://en.wikipedia.org/wiki/Storm_(event_processor)
http://hortonworks.com/hadoop/storm/
http://hortonworks.com/labs/storm/

A Storm cluster is superficially similar to a Hadoop cluster. Whereas on Hadoop you run "MapReduce jobs", on Storm you run "topologies". "Jobs" and "topologies" themselves are very different -- one key difference is that a MapReduce job eventually finishes, whereas a topology processes messages forever (or until you kill it).