There was some whole blowup with Booklore over it being vibecoded by a single maintainer recently. I think the project has changed ownership since then, but be cautious.

I use Calibre + Calibre Web. Definitely a bit old and clunky, but reliable.

Ditto for Calibre Web. Clunky, but effective.

I wish there was a way to add books to a ‘shelf’ (a collection, which you can sync to a device) without having to open each book and add. I want to go Select + Select + Select > Add > Sync.