Hi friends :D. Yes, this is one of our internal plugins that we accidentally enabled for everyone :p. It’s a reference library for many of our internal UI components :).
Storybooks are a a concept borrowed from web development. If you’re interested in adopting storybooks for your own UI development, there are some great open source storybooks such as flipbook that you can check out!
Note that you can only make stories if you are using a UI library like react-lua or Fusion. Most of Roblox’s UI is built using react-lua. If you want to learn more about react-lua, I recommend checking out my guide (also published as a staff article).
I wouldn’t read too much into the stories that are listed in the plugin. Even if you are wanting to reverse engineer our UI as we’re in the middle of revamping a bunch of things so what you’re looking at may already be out of date.