LibriVox - free public domain audiobooks
Khan Academy - Khan Academy offers online tools to help students learn about a variety of important school subjects. Tools include videos, practice exercises, and materials for instructors. Read more about Khan Academy.
Audible - Audible is the world’s largest provider of premium audiobooks and spoken word content.
edX - Best Courses. Top Institutions. Learn anytime, anywhere.
Mobilism.org - A home for book lovers, app enthusiasts, and much more.
Wikibooks - Wikibooks is a Wikimedia community creating a free library of educational textbooks that anyone can edit.