Flinto - The prototyping tool designers have been waiting for.
Base UI Sketch Framework - Huge set of everything you need to design and prototype
UiSketcher - Easily sketch user interface with your pen-enabled device!
Glyphy - Copy & paste fancy fonts + cool symbols ☞✺✐™
SketchCasts - A weekly screencast, all about how to use Sketch
Enzyme - Enzyme is a JavaScript testing utility for React.