Node.js is a platform for running server-side applications built with JavaScript. It is trivial to create a web-server instance, for example, that receives and responds to HTTP requests using callback functions.
Server-side JS isn't exactly the same as its more familiar client-side counterpart, but you'll find a lot of similarities in the same comfortable syntax that you know and love. We won't actually be writing any server-side JavaScript in this project – all we need Node for is to run the Grunt.js build tool.
To get the appropriate installer for your platform, visit the Node.js website at http://nodejs.org and hit the download button. The correct installer for your platform, if supported, should be auto-detected.