Updated May 26, 2017: Version 1.4 “The UI Kit is now updated for Sketch 44 with the new auto layout system. Therefore it also requires Sketch 44 or newer.”
macOS Sierra UI Kit (for Sketch) by Alexander Käßner. The Sketch document uses the latest features like Text Styles, Symbols and Auto Layout. You can download this for FREE and use it to create your own retina ready designs!