> [Calibre] never really adapted into the whole self-hosted era

Could you explain that in more detail? It seems to me that Calibre is totally self hosted.

I give an example. I use Calibre to import ebooks as epub (if they are not already epub, which they usually are,) maybe change their metadata and add a cover if they don't have one. The books go to Calibre's directory and then I sync to my phone using syncthing, like everything else I exchange between my laptop and my phone. I know that Calibre has a way to send books to devices but I think that it requires either a hardware reader or some interoperable app. I prefer working only with the file system. It always works no matter what I have on my phone.

All of that seems self hosted to me, or do you mean having a server somewhere at home or on the internet with the ebook collection?

I also use the editor to fix typos or to create ebooks from text files.