Get UI Kit is a lightweight and modular front-end framework for developing fast and powerful web interfaces.
Material Design Kit Android UI Kit contains interface components and 61 great screens from Android 7.0 Nougat, made with Material Design Guidelines.
Inside Design by InVision offers free design resources including high-quality UI kits, icon packs, mockups and more.
Shards is a free and modern UI toolkit for web makers based on the popular Bootstrap 4 framework. It’s lightweight, responsive and well documented.