Kavita vs Readarr

Kavita and Readarr are both open source programs for organizing e-books and comics. They can parse covers and metadata, display the library as a mosaic in a web interface, support simultaneous access by several users (and creation of several libraries). Both programs are installed on a local server and require some technical knowledge to configure.

But Kavita is focused on reading comics, manga and novels (therefore it has excellent support for CBZ, CBR, PDF, EPUB formats). Kavita has a convenient web reader that works even in a mobile browser. It works quickly and is better suited for large libraries. It has many tools for flexible organization of collections and series, but a minimum of integration with external services

Readarr is an organizer whose main feature is automation of downloading books via torrents and usenet. Apparently, that is why it was closed and the project is not officially developed. Therefore, if you download the code somewhere, check it first with an antivirus. Readarr integrates with services like Goodreads and monitors new books from your favorite authors (like Radarr/Sonarr). It's more for collecting your library than organizing it. It doesn't have a reader at all.