Flinto - The prototyping tool designers have been waiting for.
Sketch Tricks - Articles for Sketch
Base UI Sketch Framework - Huge set of everything you need to design and prototype
The Good Workshop - TGW helps experts plan, run, and track UX, CX, Product and innovation workshops, fully automated and straightforward user experience.
Glyphy - Copy & paste fancy fonts + cool symbols ☞✺✐™
Git Sketch Plugin - Version control for designers