Booksonic aka Popeens Subsonic is a fork of the music streaming server Subsonic but with a twist. While Subsonic and as far as I know all the other forks out there are focused on music, Booksonic, as the name suggests is focused on audiobooks.
Project homepage: http://booksonic.org/
Booksonic Android app: https://github.com/popeen/Popeens-DSub/