OpenStax is a virtual library of open-source e-textbooks that are available for free to students in the United States. Several websites, including Chegg.com, Vitalsource.com and textbooks.com, offer a wide selection of digital textbooks that students can search by ISBN, title or author. Vitalsource boasts a downloadable textbook reading app, so students can access their books on any device and also access their textbooks.com purchases anytime -- even offline. Books from Chegg, however, are only accessible with an Internet connection.
Bookboon.com is a sponsor-based company based in Europe that offers free digital books and textbooks available in downloadable PDF format. As of 2015, bookboon.com has more than 900 free titles available for students around the world.
Rice University's online repository, OpenStax, operates under two key premises: there should be no copyrights on knowledge, and everybody has access. The books are open-source, meaning they are not specific titles by large publishers such as McGraw Hill. Instead, books are available by college-level subjects, such as anatomy and physiology, psychology, pre-calculus and U.S. history, and they are all free. Educators have developed and peer-reviewed these books to provide accurate content that meets the scope and sequence requirements of college courses around the nation. This concept differentiates OpenStax from most other digital textbook providers.