There are Styling Systems, and there are Component Libraries…

Some component libraries come with an opinionated styling system. Others are agnostic.
Styling systems
Component libraries

There are also low-level libraries that help to make your own components.

And independent components that are not an entire library, but maybe worth installing: rehype-pretty-code.netlify.app

Most companies choose to build their own component library:

Manage your own library

A library of icons is very useful:

Icon components

And lets not ignore the upcoming no-code/low-code platforms!

Low-code development