One of the important reasons behind the origin of Node.js was to support real-time web applications. Node.js has a couple of frameworks built for real-time web applications which are hugely popular: Socket.io and Sock.JS. These frameworks make it very simple to build instant, collaboration-based applications such as Google Drive and Mozilla's together.js. Before the introduction of WebSockets in the modern browsers, this was achieved via long polling, which was not a great solution for real-time experience. While WebSockets is a feature that is only supported in modern browsers, Socket.io acts as a framework, which also features seamless fallback implementations for legacy browsers.