Base UI Sketch Framework - Huge set of everything you need to design and prototype
Sketch Confetti - Generate gorgeous confetti patterns in 1 click.
INSTAD.IO - Automagically converts vector images into sketchy style
Atomize - The most advanced Design System for Sketch
Sketch Extensions - An official collection of Sketch extensions & plugins
Merge Duplicate Symbols - Automatically find and act on duplicate symbols in Sketch