If you want to create your own design systems / UI components and want to have a simple place to show that without any actual apps running ( or as some have mentioned, without any data - related logic ), Storybook makes this easy and clean. You can build it right off from your actual application.

The company I work for uses it for frontend devs (who are mostly freelance) to understand the feel of the UI designs and how the components should be built/used.

You can see lots of showcases here: https://storybook.js.org/showcase