All kinds of useful, additional components which are not included in UIkit itself.
UIkit offers some advanced components that are not included in the UIkit core framework. Usually you wouldn't use these components in your everyday website. They include stuff like nestables and datepickers, which will come in handy, if you create advanced user interfaces like administration areas.
After you've downloaded UIkit, you can find all additional components in separate
UIkit provides test files for every component. Each of these pages contains test cases of its component and gives you an overview of all the possibilities that are supported out of the box.