For filesystem-based routing, you can take a look at Routify.
For an official solution, there's nothing that's simply a routing library. There is, however, the official Sapper framework, a Next.js-style application framework built on Svelte, which also uses filesystem-based routing.
These are 2 improvements to FAQ questions on here.
@Conduitry I don't think I can PR for the wiki functionality, so posting these here, hoping you want to make the edit 🙏
Is there a UI component library?
There are several UI component libraries. Find them under in the code section of the Svelte Community website.
Is there a router?
You can use any router lib you want. A lot of people use page.js. There's also navaid, which is very similar.
If you prefer a declarative HTML approach there's svelte-routing.
If you need hash-based routing on the client side, check out svelte-spa-router, or abstract-state-router, a mature router for business software.
For filesystem-based routing, you can take a look at Routify.
For an official solution, there's nothing that's simply a routing library. There is, however, the official Sapper framework, a Next.js-style application framework built on Svelte, which also uses filesystem-based routing.