With Lit you can build full apps with standard and plain JS, CSS, and HTML; standard web components; and no build tools.
I don't immediately see how this is any more standards-first, especially when it mentions Markdown, tooling, and a CLI. I don't actually really see what exactly this even is from this landing page. It would help to show something up front.
[1]: https://lit.dev
But the issue is that Lit still approaches web development through the lens of components. While these components may be "standard" web components that encourages developers to keep bundling markup, styles, and behavior together rather than maintaining proper separation of concerns.
Nue takes a different approach by removing all the unnecessary layers between the developer and web standards. Where Next.js forces content into JavaScript components and requires complex build pipelines, Nue provides a more direct development experience built directly on HTML (layout), Markdown (content), vanilla CSS, and vanilla JavaScript.
With Nue HMR completes in milliseconds rather than seconds. The HMR spans css, content, data, and HTML-based server and client-compnents. CSS updates instantly through the native cascade instead of rebuilding components. The entire development feedback loop stays under 100ms, maintaining perfect flow while preserving document state.
Most importantly, this sort of standards-first architecture enables true systematic design trough vanilla CSS. Instead of coupling design decisions to components through utility classes or CSS-in-JS, with Nue you can build design systems directly with CSS variables, calc() and other modern goodies.
Why is this a problem? Reuse is incredibly important for building almost anything on the web, and it's been with us since long before the web platform supported it natively, e.g. with CGI scripts that used Perl functions, to output repeated HTML "components", or PHP, web frameworks, etc.
If you don't have some method of reuse in the platform or framework, developers either have to copy-and-paste (and deal with so many difficulties of updating and maintaining consistency that it's not a realistic option), or push reuse to a non-standard layer of the system like server templating.
Server templating is fine, but it doesn't actually get rid of the implicit concept of components that'll be in the page or app, it just disaggregates it among to non-colocated parts of the system.
Web components can be written in standard JS modules, loaded by or inlined into standard HTML, instantiated by standard custom element tags, rendered with the help of standard <template> elements, and styled with standard CSS.
If you don't use the web platform's native facilities for re-use, then you do have to use some non-web-standard system, like a server framework. Is there some way you see that that's more standard than the web?
Your Markdown- based content generates semantic HTML. Your styling is pure CSS with modern features like nesting and container queries. JavaScript remains vanilla JavaScript.
React and similar frameworks introduce non-standard abstractions like JSX and proprietary component models that deviate from web standards. They couple structure, styling and behavior into JavaScript components.
With Nue your codebase becomes primarily CSS-based, with clean separation between content, styling and behavior. You're working directly with CSS rather than through framework abstractions. Hopefully this FAQ answers most of your questions:
The problem with Markdown is there is no standard.