It includes basic components: boxes, text boxes, text input, buttons, sliders, radio and multiple selection buttons, and color selecter. And layout components: vertical and horizontal stacks, dropdowns, a topbar and a scrollable container.
It can be useful to test game mechanics or to build app interfaces.
You can use this cart and see how it works or check the documentation on the github repository.
(I'll try to make a video on how to use it and post it here too :))
Here's one simple example: