Webpack is a module bundler that can be configured (in various config files) to do pretty much anything you want: Compile all your CSS/JS/LESS files in a single file, Compile your CSS/LESS/JS in seperate files for vendor code/your code, Minify, Parse JSX files, Hot module replacement on their integrated web server, etc.

node.js is a Javascript runtime that allows you to execute javascript on your local machine or a server. npm is the package manager for node/js and makes it a breeze to take care of your projects dependencies. I use node.js (more specifically express.js) in my stack to handle http requests and proxy them to local/remote files and databases.

React.js is a Javascript library that makes it very easy to build interfaces. It re-renders itself when the data that's relevant to the component has been updated, and only renders the HTML that was changed - courtesy of the VirtualDOM. It utilises a uni-directional data-flow which is an interesting approach to data-binding.