Audible - Audible is the world’s largest provider of premium audiobooks and spoken word content.
LibriVox - free public domain audiobooks
LearnOutLoud.com - LearnOutLoud.com is the web's largest resource for audio & video learning.
Hoopla Digital - Audio books, movies, music, and ETC. Very similar to libby.
Audiobook Bay - Download unabridged audiobook for free or share your audio books, safe, fast and high quality!
Libro.fm - A digital audiobook platform for independent bookstores