Flowkit - Sketch library for user flows/content maps/annotations
Eva Design System - A free customizable design system
Crystal: Sketch Mirror for Android - Crystal: Sketch Mirror for Android is an application that is designed for viewing your sketch designs in real-time, navigate prototypes and download content related to the sketches for offline viewing.
Sketch 101 by Designlab - Learn Sketch in this free course w/ downloadable templates
Figma Mirror - Figma Mirror is an application that covers top trending designing or sketching ideas making your teamwork in a single environment and design better products from start to finish.
Sketch Repo - Collection of resources for anyone who uses Sketch