Base UI Sketch Framework - Huge set of everything you need to design and prototype
INSTAD.IO - Automagically converts vector images into sketchy style
UiSketcher - Easily sketch user interface with your pen-enabled device!
Sketch Extensions - An official collection of Sketch extensions & plugins
SketchCasts - A weekly screencast, all about how to use Sketch
Graphcool - The GraphQL backend for mobile & web developers to build better apps faster ⚡️