What is the point/purpose of Ruby EventMachine, Python Twisted, or JavaScript Node.js?
- by CCw
I don't understand what problem these frameworks solve.  Are they replacements for a HTTP server like Apache HTTPD, Tomcat, Mongrel, etc?  Or are they more?  Why might I use them... some real world examples?  I've seen endless examples of chat rooms and broadcast services, but don't see how this is any different than, for instance, setting up a Java program to open sockets and dispatch a thread for each request.
I think I understand the non-blocking I/O, but I don't understand how that is any different than a multi-threaded web server.