Flowkit - Sketch library for user flows/content maps/annotations
UI Garage - Specific mobile and web design patterns for your inspiration
Sketch 101 by Designlab - Learn Sketch in this free course w/ downloadable templates
UI Movement - The best UI design inspiration, daily
Sketch Basics - First official Sketch course on Treehouse
Daily UX Challenge - Improve your UX skills with a challenge posted each day 🛠️