I’m making Stacks, an open source ebook manager and server, as a lightweight alternative to Calibre.
Written in Swift, it consists of a SwiftUI browser and a Mac/Linux server and CLI. Shares are automatically discovered via Bonjour/avahi and also published as OPDS feeds.
It can import Calibre libraries and has basic support for managing books on Kindles, but I’ve only tested it with a MTP Paperwhite as that’s all I’ve got.
I’m quite interested in this. Where are you getting metadata and covers from? I found this pretty hard unless you pay for ISBNdb (OpenLibrary has bad covers, and Google Books API doesn’t give you high resolution ones I think).