CSS Tools

Desktop & mobile CSS frameworks:
Mobile only CSS frameworks:
CSS reset:

A CSS Reset (or “Reset CSS”) is a short, often compressed (minified) set of CSS rules that resets the styling of all HTML elements to a consistent baseline. - http://cssreset.com/

Transpiling:
References:
Linting/hinting:
Code formatter/beautifier:
Optimizer:
Online creation/generation/experimentation tools:
Architecting CSS:
Authoring conventions:

https://github.com/trending?l=css&since=monthly