The Assayer - catalog of books whose authors have made them available for free; users can also submit reviews
bookboon.com, Download free eBooks and textbooks - over 1000 free eBooks for university students and business professionals; can be downloaded directly in PDF format; currently available in seven languages
collegeopentextbooks.org, Open Textbooks - collection of twenty-nine educational non-profit and for-profit organizations, affiliated with more than 200 colleges, is focused on driving awareness and adoptions of open textbooks to more than 2000 community and other two-year colleges
Freebookcentre.net - links to free online technical books; either downloadable or can be viewed online; collections include core Computer Science, Electronics, Science, Medical
FreeTechBooks - lists free online computer science, engineering and programming books, textbooks and lecture notes, all of which are legally and freely available over the Internet
Internet Archive, Ebook and Texts - Download free books and texts, wide range of fiction, popular books, children's books, historical texts and academic books
Minnesota University, Open Academics - catalog of open textbooks to be reviewed by faculty members: Accounting & Finance, Business, Management & Marketing, Computer Science & Information Systems, Economics, General Education, Humanities & Language, Math & Statistics, Natural & Physical Sciences, Social Sciences
Open Access Textbook - Websites; definitions of what constitutes an open textbook varies among sites
Open Book Project - aimed at the educational community; seeks to encourage and coordinate collaboration among students and teachers for the development of high quality, freely distributable textbooks and educational materials on a wide range of topics
Open Library - open, editable library catalog, building towards a web page for every book ever published
OpenThesis.org - free repository of theses, dissertations, and other academic documents; search, organization, and collaboration tools
OpenStax College - nonprofit organization committed to improving student access to quality learning materials; free textbooks developed and peer-reviewed by educators to ensure they are readable, accurate and meet the scope and sequence requirements
Project Gutenberg - offers over 50,000 free ebooks; epub & free kindle books, download or read online.
Textbook Revolution - student-run site dedicated to increasing the use of free educational materials, links and reviews of textbooks and select educational resources, Some books are PDF files, others viewable online as e-books
textbooksfree.org - Free Textbooks and/Course Notes, Free Courses, Economics of College Texts, Publishers Fight Back, Free Internet Libraries, Education Libraries, Textbook Development Sites (Completed Textbooks, helpful text materials), Textbooks Adoption Plan, Improving Free/Open Textbooks, Interesting Ideas, Free Textbooks Advocates, Interesting Reading
Wikibooks - open-content textbooks collection that anyone can edit: Science, Social sciences, Languages, Mathematics, Miscellaneous, Computing, Engineering, Humanities
Wikipedia-Books - collection of Wikipedia articles that can be easily saved, rendered electronically in PDF, ZIM or OpenDocument format, or ordered as a printed book