It's the same general wheelhouse of documentation tools as mdbook, i.e. take a pile of markdown and produce high quality documentation. One of the standout features of Docusaurus is that it's based on React so it builds a SPA for your documentation (while still being good about pre-rendering, etc. for good SEO). If you load up a Docusaurus site and start clicking around to read docs it feels like a native app without clunky refreshes, etc. It's very extensible and can be turned into very custom and slick documentation portals.

It also supports MDX which is a a version of markdown that embeds React controls and allows interesting client-side interactivity in your documents. This is very handy for frontend libraries and tools which typically have a showcase or component library which you can interact directly from the docs.