Apache Storm is a free and open source distributed realtime
computation system.  Storm makes it easy to reliably process
unbounded streams of data, doing for realtime processing
what Hadoop did for batch processing. Storm is simple, can
be used with any programming language, and is a lot of fun
to use!

Storm has many use cases: realtime analytics, online machine
learning, continuous computation, distributed RPC, ETL, and
more. Storm is fast: a benchmark clocked it at over a
million tuples processed per second per node. It is
scalable, fault-tolerant, guarantees your data will be
processed, and is easy to set up and operate.

WWW: http://storm.incubator.apache.org/