Mozilla Style Guide
Design Systems, Style Guides, Pattern Libraries
OS X Human Interface Guidelines: Designing for Yosemite
Style Guide
BBC - GEL (Global Experience Language)
Grid System | MailChimp
Design patterns
U.S. Web Design Standards | U.S. Web Design Standards
Lightning Design System
Harvard Law Review: Style Library
SC5 Style Guide Generator
Pattern Language: Responsive Style Guides
a brand new styleguide: Elements
Pattern Library
lonelyplanet/rizzo
Style Guide | Una Kravets
A SASS Style Guide - Ackmann & Dickenson
Website Style Guide Resources