Flinto - The prototyping tool designers have been waiting for.
Neovidya - Neovidya provides structured access to high-quality educational content.
Base UI Sketch Framework - Huge set of everything you need to design and prototype
Flowkit - Sketch library for user flows/content maps/annotations
Glyphy - Copy & paste fancy fonts + cool symbols ☞✺✐™
Sketch Tricks - Articles for Sketch