Astro is a metaframework that among others can use Svelte for both static and interactive components. Plain Svelte without a metaframework is not suitable for normal websites with multiple pages, but Astro is.
As for Astro vs SvelteKit, I generally prefer Astro's approach to filesystem based routing (no +page etc.), I prefer it's MPA approach to the clientside routing SvelteKit and others use OOTB, I like that it's very tailored towards content and being an SSG (content collections, MD and MDX support ootb, currently experimental automatic image optimization), and the "integrations" are a huge time-saver. Some common ones you can add with `astro add`, and many others are just a quick config edit away.
I recently built a pretty performant portfolio site with Astro in a single day using DecapCMS and UnoCSS, both as integrations, all the client had to do was accept the invite from Netlify Identity and start adding content to their site!
As for Astro vs SvelteKit, I generally prefer Astro's approach to filesystem based routing (no +page etc.), I prefer it's MPA approach to the clientside routing SvelteKit and others use OOTB, I like that it's very tailored towards content and being an SSG (content collections, MD and MDX support ootb, currently experimental automatic image optimization), and the "integrations" are a huge time-saver. Some common ones you can add with `astro add`, and many others are just a quick config edit away. I recently built a pretty performant portfolio site with Astro in a single day using DecapCMS and UnoCSS, both as integrations, all the client had to do was accept the invite from Netlify Identity and start adding content to their site!