Design Principles - An open source repository of design principles and methods
Porsche Design Book One - The ultimate notebook experience from Porsche
Product Disrupt - A design student's list of resources to learn Product Design
Upcase by thoughtbot - An online learning platform for developers - now free
Colorbox.io - Create accessible color systems 🎨
Design Systems Handbook by DesignBetter.Co - Your guide to design systems best practices