Global Text Project: The Global Text Project is an open educational resources that creates and translates open content textbooks and makes them freely available online. Global Text Project is a non-profit organisation which aims to eliminate the prohibitive cost of textbooks and make education accessible to everyone, regardless of income, location, or any other factor. The organisation focuses on reaching people of university-going age in the developing world. Founded in 2006, the Global Text Projects has made over 100 textbooks available for free online, many of which have also been translated into a variety of other languages.
IntechOpen: A multidisciplinary Open Access publisher of books and journals covering the fields of Science, Technology and Medicine. InTech has published more than 850 Open Access books, and provides support services for faculty who wish to publish a book or journal and make it available via Open Access.
JSTOR Open Books: A collection of over 6,000 Open Access DRM-free ebooks from a variety of academic publishers with coverage in many disciplines including Business, Anthropology, Education, Environmental Science, Health Sciences, History, Law, Political Science, Religion, Psychology, Technology and more!
Wikibooks: Almost 3000 open-content textbooks that anyone can edit. "Wikibooks is for textbooks, annotated texts, instructional guides, and manuals. These materials can be used in a traditional classroom, an accredited or respected institution, a home-school environment, as part of a Wikiversity course, or for self-learning. As a general rule, only instructional books are suitable for inclusion. Non-fictional books (as well as fictional ones) that aren't instructional aren't allowed on Wikibooks. Literary elements, such as allegory or fables, that are used as instructional tools can be permitted in some situations."