mp3 of books (many for free, including classics like "Call of the Wild" and "Anne of Green Gables." You have to sort through their categories, which are topic based rather than genre. Looks like it might have some potential, though recent books (e.g., biography of Steve Jobs) cost money.
You can turn a doc, PPt and more into an interactive book. I see lots of potential here if you write books with students that are then shared with families. Free, of course!
Don't think I've ever read a stronger review of a book. I bought it and read it and whole heartedly agree. Don't launch your wtg wkshp without this book!
Something to consider--open source ebooks from Press Books. You need to install WordPress Multisite (important). Caution: do not use with existing WordPress site.