Base UI Sketch Framework - Huge set of everything you need to design and prototype
Sketch Confetti - Generate gorgeous confetti patterns in 1 click.
SketchCasts - A weekly screencast, all about how to use Sketch
Atomize - The most advanced Design System for Sketch
UiSketcher - Easily sketch user interface with your pen-enabled device!
Merge Duplicate Symbols - Automatically find and act on duplicate symbols in Sketch