Sass - Syntatically Awesome Style Sheets
Darkness: Beautiful Dark Themes - Chrome extension that provides beautiful dark themes for Facebook, Google and more.
PostCSS - Increase code readability. Add vendor prefixes to CSS rules using values from Can I Use. Autoprefixer will use the data based on current browser popularity and property support to apply prefixes for you.
f.lux - f. lux is a piece of software for Windows, Mac, Linux, iOS, and Android that provides a blue light filter over your screen. Research suggests limiting our exposure to blue light in the hours before bedtime can help us fall asleep faster.
Stylus - EXPRESSIVE, DYNAMIC, ROBUST CSS
Stripe Atlas - The best way to start an internet business