Node.js provides an event-driven architecture and a non-blocking I/O API designed to optimize an application's throughput and scalability for real-time Web applications. It uses Google V8 JavaScript engine to execute code, and a large percentage of the basic modules are written in JavaScript. Node.js contains a built-in library to allow applications to act as a stand-alone Web server.
Node.js is used by GoDaddy, Groupon, IBM, LinkedIn, Microsoft, Netflix, PayPal, Rakuten, SAP,Voxer, Walmart, and Yahoo!.
Node.js is typically used where light-weight, real-time response is needed, like communication apps and Web-based gaming. It is used to build large, scalable network applications.

