Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.
Rewireify is a port of Rewire for Browserify that adds setter and getter methods to each module so that their behaviour can be modified for better unit testing.