openstax (free textbook website).

There is a website called openstax .org which provides the free text book.                 

openstax is a nonprofit educational technology initiative based at Rice university. Since 2012 , openstax has created peer - reviewed , openly - licensed text books , which are available in Kindle versions on Amazon.com and in the iBooks store. Openstax also launched openstax tutor beta , machine learning , and openstax content.                                                                                                                        Aiming to compete with major publishers' offerings, the project was initially funded by the Bill and Melinda gates Foundation, the William and flora Hewlett foundation, the Michelson 20MM foundation , and the Maxfield Foundation. All textbook content is licensed under Creative commons Attribution licenses ; specifically, the books are available under the CC BY license (except for Calculus, which is CC BY-NC-SA), which means that instructors are able to use, adapt, and remix the content, as long as they attribute OpenStax.

In 2017, OpenStax announced that they were partnering with UK Open Textbooks to spread the use of their open content in the UK, and partnering with Katalyst Education to form OpenStax Polska, bringing Polish-language versions of select OpenStax books to universities in Poland.