Base UI Sketch Framework - Huge set of everything you need to design and prototype
Product Frameworks - Discover product frameworks used to help build products
UiSketcher - Easily sketch user interface with your pen-enabled device!
Startup Rocket Framework - Framework to help entrepreneurs w/ the first critical steps
SketchCasts - A weekly screencast, all about how to use Sketch
Craftwork - A collection of User Interface resources made by Craftwork