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
Remake - A way to make web apps with just HTML & CSS
Merge Duplicate Symbols - Automatically find and act on duplicate symbols in Sketch