FediBooks runs on Windows, macOS, and Linux. It works with instances running Mastodon, Pleroma, Misskey, and more. You won't have to worry about whether or not FediBooks will work with your setup — it's designed to be compatible with it all.
FediBooks is licensed under the GNU AGPLv3, a libre, copyleft license. This means that it will always be not only free of charge, but also free to distribute, free from access restrictions, and free to modify. However, you must provide attribution when using FediBooks to run your bot.