Sketch Repo - Collection of resources for anyone who uses Sketch
PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
AT-UI - UI library for developing powerful web interfaces
Zeplin - Collaboration app for UI designers & frontend developers
UI Libraries by Shuffle - A marketplace for busy front-end developers
Base UI Sketch Framework - Huge set of everything you need to design and prototype