Sketch 101 by Designlab - Learn Sketch in this free course w/ downloadable templates
Anima App - Design, get feedback, convert to code, publish, iterate.
Sketch Tricks - Articles for Sketch
Sketch Repo - Collection of resources for anyone who uses Sketch
The Design Thinking Workshop Kit - A free digital and print kit to help run your own workshop
Auto-Layout for Sketch - Responsive design for Sketch