I notice that you specifically mentioned audiobooks, but if you're interested in written ebooks, check out Standard EBooks

They take public domain books and run them through a detailed process of editing and typesetting them to create beautiful versions.

Personally, I'm a big fan of The Personal Recollections of Joan of Arc by Mark Twain. There is an audiobook version on Librevox too!

Lots of communities on the federated lemmynsfw.com server