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...
Sprite Cow : Sprite Cow helps you get the background-position, width and height of sprites within a spritesheet as a nice bit of copyable css.
Sizzy : A tool for developing responsive websites crazy-fast.
Open sourced : https://github.com/kitze/sizzy
Autoprefixer : PostCSS plugin to parse CSS and add vendor prefixes to CSS rules using values from Can I Use.
Online javascript beautifier : Beautify, unpack or deobfuscate JavaScript and HTML, make JSON/JSONP readable, etc.