The DOAB Is an online discovery tool that enables users to search and find Open Access books, which you the user can then download from the site of the publisher. All books in DOAB have a full open access licence, making them 'free to share'. You can link books found through the DOAB to your module's online reading list.
Project Gutenberg is a library of over 60,000 free eBooks, which can be downloaded or read online. You will find the world's great literature here, with focus on older works for which U.S. copyright has expired.
MUSE provides access to a growing list of scholarly open access content, including over 600 open access (OA) books from several distinguished university presses and scholarly societies.
Haithi Trust preserves 17+ million digitised items - the largest set of digitised books managed by academic and research libraries under the aims of scholarly, not corporate, interests.
"Open textbooks are textbooks that have been funded, published, and licensed to be freely used, adapted, and distributed. These books have been reviewed by faculty from a variety of colleges and universities to assess their quality. These books can be downloaded for no cost, or printed at low cost.The library currently includes 749 textbooks, with more being added all the time." (Open Textbook Library)
Open Stax provide access to peer-reviewed, openly licenced free textbooks, covering a range of subject disciplines such as mathematics, humanities, social sciences, business and more. There are also support learning resources to accompany textbooks.