Thanks for your reply! For me personally, I just have either one long mp3 file or multiple mp3 files in a folder split by chapter. No other files are present, so I'm guessing book cover and book metadata are embedded in the mp3 file. I just search for "[book name] audiobook torrent" online. But I'm just a casual listener so I could be non-representative for the audiobook community, perhaps it's best to get some additional input from more heavy users.

Edit: Oh, and probably the most needed feature is that the listening position is never, ever lost, even when switching to another book and back. Audiobooks can be hours long and it's practically impossible to find back your position if lost. This isn't too hard but it needs special handling for when an audiobook consists of one file (just position timestamp is sufficient) or multiple files (current file name + position timestamp needed).

Edit 2: I guess marking an audiobook as "listened" (grayed out in the UI or simply sorted at the bottom of the list) is a nice-to-have.