Node.js is an open-source, cross-platform JavaScript runtime environment that allows developers to create both front-end and back-end applications using JavaScript. It was released in 2009 by Ryan Dahl and is built on top of the Chrome V8 JavaScript engine. Node.js is designed to build scalable network applications and is an asynchronous event-driven JavaScript runtime. It uses an event loop as a runtime construct instead of as a library, which makes it different from other systems. Node.js is single-threaded, non-blocking, and uses an asynchronous, event-driven model, which makes it efficient and suitable for real-time applications.

Node.js is free and runs on various platforms such as Windows, Linux, Unix, and Mac OS X. It is well-suited for building I/O intensive applications like video streaming sites and online chatting applications. Node.js is also capable of handling a huge number of simultaneous connections with high throughput, making it scalable.

Node.js is written in C, C++, and JavaScript and eliminates the waiting time for tasks like opening and reading files on the server. It uses asynchronous programming, which makes it very memory efficient. Node.js can generate dynamic page content, create, open, read, write, delete, and close files on the server, collect form data, and add, delete, and modify data in your database.

In summary, Node.js is a powerful tool for building scalable network applications using JavaScript. It eliminates the waiting time for tasks and is efficient and suitable for real-time applications. It is free, runs on various platforms, and is well-suited for building I/O intensive applications.