LibriVox - free public domain audiobooks
Audible - Audible is the world’s largest provider of premium audiobooks and spoken word content.
Hoopla Digital - Audio books, movies, music, and ETC. Very similar to libby.
OverDRIVE - Make workspaces and sites automatically from Google Drive
DigitalBook.io - Free audio books and eBooks. Search, browse, listen, read and download over 100,000 free audio books and eBooks.
Libro.fm - A digital audiobook platform for independent bookstores