Base UI Sketch Framework - Huge set of everything you need to design and prototype
Frames for Sketch - Create awesome websites & apps using powerful design system
SketchCasts - A weekly screencast, all about how to use Sketch
Sketch Repo - Collection of resources for anyone who uses Sketch
UiSketcher - Easily sketch user interface with your pen-enabled device!
Merge Duplicate Symbols - Automatically find and act on duplicate symbols in Sketch