ebook converter functionality

The ebook converter functionality from Calibre is top notch, and I haven't really found an alternative (this stack overflow question about lightweight alternatives remains unanswered: https://unix.stackexchange.com/questions/414712/lightweig...), pandoc doesn't seem to support .mobi either.

The closest I've found in terms of a lightweight format conversion library is this repo: https://github.com/gryf/ebook-converter, which takes the format conversion code from an old version of calibre as a standalone application. Works for me, but I feel kind of sad that there aren't better versions.