OPEN TEXTBOOKS

http://openstaxcollege.org

OpenStax College
http://openstaxcollege.org

Initiated by Rice University, their free textbooks are developed and peer-reviewed to ensure they meet the scope and sequence requirements of college courses.

http://www.saylor.org/books/

Saylor Academy
http://www.saylor.org/books/

Collection of freely available open textbooks for download, online reading, and sharing.

https://libretexts.org/

LibreTexts
https://libretexts.org/

The LibreTexts mission is to unite students, faculty and scholars in a cooperative effort to develop an easy-to-use online platform for the construction, customization, and dissemination of open educational resources (OER) to reduce the burdens of unreasonable textbook costs to our students and society.

https://www.doabooks.org/

Directory of Open Access Books
https://www.doabooks.org/

The Directory of Open Access Books (DOAB) is a discovery service for Open Access monographs. 

https://open.umn.edu/opentextbooks

The University of Minnesota Open Textbook Catalog
https://open.umn.edu/opentextbooks

This site is a clearinghouse of links to books housed in various locations, including OpenStax, Saylor and others, with over 140 books.

http://www.collegeopentextbooks.org/

College Open Textbooks
http://www.collegeopentextbooks.org/

Focused on driving awareness and adoptions of open and peer-reviewed textbooks to more than 2,000 community colleges.

https://open.bccampus.ca/find-open-textbooks/

BC Campus OpenEd
https://open.bccampus.ca/find-open-textbooks/

This collection includes texts written specifically for the BC OpenTextbook initiative. 

http://www.nap.edu/

The National Academies Press
http://www.nap.edu/

Unlike some of the open textbook initiatives these books are publicly available but not openly licensed.  You can link to the content, and even link directly to specific pages.  However, you cannot remix and redistribute the content.

https://www.textbookequity.org/the-textbooks/

Textbook Equity
https://www.textbookequity.org/the-textbooks/

Creator, publisher, distributor, and seller of open textbooks and ancillary materials to college-level students.

FreeTechBooks
https://www.freetechbooks.com/

Database of Free / Open Access Online Computer Science Books, Textbooks, and Lecture Notes.

http://bookboon.com/

Bookboon
http://bookboon.com/

European eBook publisher with 1000+ textbooks freely available to download. E-books are primarily in business/economics, engineering/natural sciences and IT.

http://www.opentextbooks.org.hk/

Open Textbooks for Hong Kong
http://www.opentextbooks.org.hk/

The Open Textbooks for Hong Kong project aims to establish a sustainable system which provides quality open textbooks for adoption and adaptation at minimal cost for education for all.

Open Access Books on JSTOR
https://about.jstor.org/librarians/books/open-access-books-jstor/

More than 6,500 Open Access ebooks from 90 publishers, including Brill, Cornell University Press, De Gruyter, and University of California Press, are now available at no cost to libraries or users.

WIKIBOOKS
http://www.wikibooks.org/

Wikibooks is a collection of open-content textbooks.

Project Gutenberg
http://www.gutenberg.org/

Project Gutenberg is an online library of free eBooks.

American Institute of Mathematics
http://aimath.org/textbooks/approved-textbooks/

AIM’s mission is to advance mathematical knowledge through collaboration, to broaden participation in the mathematical endeavor, and to increase the awareness of the contributions of the mathematical sciences to society.

Free Books 4 Doctors
http://www.freebooks4doctors.com/

Free access to medical books.