An “open textbook,” as defined on the Open Textbook Library website, is one that has “an open license that makes it free for anyone to use and change. It can be print or digital” (FAQ). The Open Textbook Library, as of the date of this posting, has 1093 open textbooks. To browse by subject or to take a look at the newest books in the library, visit their website: https://open.umn.edu/opentextbooks.
Open Textbook Library