Now UI Kit is a responsive Bootstrap 4 kit provided for free by Invision and Creative Tim. It is a beautiful cross-platform UI kit featuring over 50 elements and 3 templates.
Shards UI Kit is a free, modern and lightweight UI toolkit based on Bootstrap 4 that comes packed with 2 extra pre-built landing pages and 11 custom components that you can use to kick-off your next project.
All of the components, layouts and typography are made according to Apple's Human Interface Guidelines. The naming convention of each component strictly follows Apple Developer Documentation so you can get familiar with it when you implement your designs in Xcode.
Tabler Email is a set of 50 mobile-ready email templates. From e-commerce messages to product newsletters, it helps you prepare emails that look perfect in any email client, on any device.
Stream UI Kit is beautiful Open Source Bootstrap 4 UI Kit under MIT license. The UI Kit comes with 5 beautiful complete pages and includes over 20 reusable and customizable UI Blocks. It’s lightweight and only ~17kb when minified.