EventMachine is a framework for network and concurrent programming, based on the Reactor design pattern. The Reactor pattern describes a service handler that receives events and dispatches them to registered event handlers. The benefits of the reactor pattern are a clear separation between the event dispatching and the application logic that handles the events, without complicating the code with multithreading.(source : http://www.infoq.com/news/2008/06/eventmachine )

http://rubyeventmachine.com/