Bloomsbury publishing features a series of Open Content materials available for the public to read free of charge online.
Project Gutenburg is a database containing books that are either free in the United States because their copyrights have expired, or are copyrighted works that the authors have given permission for them to be distributed freely, in non-commercial means. It has a wide variety of materials that could be of use as supplemental materials to an equally wide variety of courses.
Boundless (CC BY SA 3.0)
Boundless provides educators an affordable textbook alternative, offering over 100 textbooks in 20+ areas of study. The textbooks cost just $19.99 and are available online, and are customizeable by the professor. They include a system of integrated study materials, and educators have the ability to create assignments and due dates. Additionally, it provides teaching slides for use in-class.
Bookboon.com (Site-Specific Permissions)
Bookboon.com contains free eBooks and textbooks that can be downloaded as a pdf, no registration needed.
College Open Textbooks (Item-Specific Licenses)
College Open Textbooks is the initiative of a number of organizations who have made it their goal to provide free, open source textbooks online for students.
Global Text Project (Item-Specific Licenses)
The Global Text Project is a joint initiative between the Terry College of Business at the University of Georgia and The Daniels College of Business of the University of Denver. Its main goal is to publish eBooks that can be accessed by all, especially the developing world.
In Tech- Open Access Publisher (Open Access)
In Tech publishes more than 2,300 open textbooks and 6 journals in a variety of subjects that fall under the heading of science, technology, and medicine.
Open SuNY (CC BY NC SA)
Open SuNY is an open access textbook initiative of the State University of New York libraries. While its current holdings are limited, they continuing to grow. These materials are published by faculty authors with peer reviewers, and they can be distributed freely in non-commercial capacities. They can also be altered with attribution to the original source, so long as the same license is kept.
OpenStax College (CC BY 3.0)
OpenStax College is an initiative of Rice University that offers free online textbooks, or low-cost books if students desire a physical printed copy. The books can be downloaded as pdf or for eBooks, or can be read online. These books are peer reviewed, though they can be completely customized by the instructor of a given course.
Open Textbook Library (Item-Specific Licenses)
Open Textbook Library is an initiative of the University of Minnesota that provides a variety of online, open source textbooks for students.
The Orange Grove (Site-Specific Permissions)
The Orange Grove is Florida's digital repository for instructional resources. These materials are for educators to use, remix, and share to enhance their classroom instruction. As part of this, the repository has a large open source textbook database.
SmARThistory (CC BY NC SA 3.0)
SmARThistory is an online resource provided by Khan Academy, the product of collaboration by Art Historians worldwide. It is a high-quality, introductory Art History source freely available to the public, and currently offers countless photos and more than 500 videos on a variety of topics, along with the text itself.