Okay, that sound amazing, i will check if it exists as an app on true nas, otherwise I'll do my best to find a solution, though ereolen is already free if you are part of a library here in Denmark, then you can borrow a few books every month, but the interface works like shit, so it is a lot better to just download them, then you also has no cap on the amount you get
I don't know about about Danish audiobooks, but MAM is the best source I've found so far. It's a private torrent tracker but they have an official interview process you can go through for access.
Jerboa is still fairly new and hasn't implemented all the features yet. That said, Google exists. Before making my previous post I actually verified that the search would have worked for them.