Sketch Toolbox - A super simple plugin manager for Sketch
Sketch Talk - A community for Sketch users of all skill levels
SketchCasts - A weekly screencast, all about how to use Sketch
Git Sketch Plugin - Version control for designers
Sketch 101 by Designlab - Learn Sketch in this free course w/ downloadable templates
Sketch to App Store - Generate App Store images for all iPhone sizes from Sketch