* LibreTexts: A collection of open educational resources, including textbooks.
* Project Gutenberg: A large collection of free eBooks, including some textbooks.
* Google Books: Some textbooks are available for free or for purchase through Google Books.
* Amazon Kindle: Some textbooks are available for free or for purchase through Amazon Kindle.
* Barnes & Noble Nook: Some textbooks are available for free or for purchase through Barnes & Noble Nook.
* Textbook Revolution: A website that offers free and low-cost textbooks.
* Chegg: Chegg offers a subscription service that provides access to a library of textbooks and other study materials.
* Course Hero: Course Hero offers a subscription service that provides access to a library of textbooks and other study materials.