Socket.io

Socket.io is a powerful tool that allows you to bring together three different technologies and utilize them in unison.

With Socket.io you can harness all of the useful features of a socket but have the flexibility to plug your sockets in to a web server using express.

The third feature that I believe makes Sockets.io very powerful is it's ability to integrate custom event emitters and listeners a feature which native sockets are missing, unless you get extremely hacky with your code.

By brining all three of these technologies together you are able to create robust, custom, real time applications that can do almost anything you think of.