Babel.js has become the default compiler for writing next-generation JavaScript. Its ecosystem is really taking off, thanks to its restructured plugin system. It allows developers to write ES6 (and even ES7) code that runs in the browser or in the server without sacrificing backward compatibility for older browsers, and with very little configuration. It has first-class support for different build-and-test systems, which makes integration with any current workflow simple. It is a great piece of software that has become the main driver of ES6 (and ES7) adoption and innovation.