I've checked 3 other kits on sketchappsources.com (not to say the one that comes with Adobe XD — it's very basic). This one is more polished by far. By far!

Hey, producthunters! 🤘 Proud to introduce you Material Design Kit – library of UI elements, app templates, and style guides combined into high-quality source files for Sketch and Adobe Photoshop. What’s inside: - 250+ screen templates divided into 14 most popular Google Play categories. - Detailed and clear style guide with color palette, typography system and basic layouts. - Collection of interface elements, such as icons, search bars, alerts, tab bars, segmented controls, switches, keyboards, steppers, pickers, sliders, buttons. - Collection of UI elements & native app screens found in the latest Android Nougat release made with careful attention to Google Guidelines (available for free) All the elements are made with extra attention to Guidelines and ready to help you with any design task. Check it and try for free: https://materialdesignkit.com/. Hope you’ll love it! Here is a code for all Product Hunters – PRODUCTHUNT20, it will give you 20% discount on Material Design Kit. We’re open to your “What to add/improve” requests, so please feel free to contact us via chat on the website, or leave feedback here. @_jacksmith, thanks a lot for hunt!

Tried to download GUI kit for Sketch, but nothing there... https://gum.co/android_gui