Async-std is still actively maintained and developed.

I was under the impression that it's based on Smol, but maybe I'm wrong.

It has separate maintainers (a whole team), who will continue to maintain the parts of smol they are using. Smol is relatively small and sinple.

I think it's rather that smol is "complete" and doesn't need much maintenance.

Maybe that's true. I don't know how complex these things are, or if they will be affected by future changes in the language, but it feels weird to say that a critical piece of software is complete. I wonder if many new libraries will use Smol.

One of the principles that stjepang was very keen on for smol was that libraries shouldn't depend on it. Libraries should be written in an async-executor generic way and the end binary should then be free to use smol as the executor, or tokio, or anything else.

I'm currently using smol (in an application I'm developing - not just a library) and I don't think this will scare me away. He appears to still be responding to pull requests, and smol consists of a reasonably small amount of very high quality code.