Responsive Viewer - View multiple screen dimensions in one view
Design Principles - An open source repository of design principles and methods
Responsinator - Designed to test responsive websites on different devices.
UX Research Field Guide - Your map to the world of UX research 🌏🕵️♀️
Responsive Website Test - Test any website on desktop, mobile, and tablet
Product Disrupt - A design student's list of resources to learn Product Design