fuelux : Extends Twitter Bootstrap with additional lightweight JavaScript controls. Easy to install, customize, update, and optimize. All functionality covered...
Prettier : Prettier is an opinionated code formatter. It enforces a consistent style by parsing your code and re-printing it with its own rules that take the max...
nwb : A toolkit for React, Preact & Inferno apps, React libraries and other npm modules for the web, with no configuration (until you need it)
Babel : Babel will turn your ES6+ code into ES5 friendly code, so you can start using it right now without waiting for browser support.
DOM Monster is a cross-platform, cross-browser bookmarklet that will analyze the DOM & other features of the page you're on, and give you its bill of health.