SvelteKit is a meta framework for Svelte, bringing powerful features such as routing, server (and static) site rendering, and much more to the already popular frontend framework. Similar to how Next.js builds on top of React, SvelteKit is an extension of Svelte which makes it possible to build powerful web applications without having to think deeper about configuration, bundling and other things related to bootstrapping a project using Svelte.
Under the hood, SvelteKit uses the powerful build- and development tool Vite in order to provide a fast and reliable development experience, for instance through Hot Module Replacement (HMR) in order to instantly see changes in the browser.