Design Principles - An open source repository of design principles and methods
UXsniff - Track user behavior on your website and improve conversions with UXsniff: the user experience watchdog that looks out for you.
UX Research Field Guide - Your map to the world of UX research 🌏🕵️♀️
Uxcel - The easiest way to learn UX/UI design
UX Design Weekly - The best user experience links each week to your inbox
uEye - uEye is free, fun, and an interactive way to learn UI design.