"We publish open content electronic textbooks that are freely available from this website. We focus on content development and Web distribution, and we will work with relevant authorities to facilitate dissemination by other means when bandwidth is unavailable or inadequate. The goal is to make textbooks available to the many who cannot afford them."
HathiTrust is a partnership of major research institutions and libraries and their "aim to build a comprehensive archive of published literature from around the world . It provides long-term preservation and access services for public domain and in copyright content from a variety of sources, including Google, the Internet Archive, Microsoft, and in-house partner institution initiatives."
"The Knowledge Unlatched model depends on many libraries from around the world sharing the payment of a single Title Fee to a publisher, in return for a book being made available on a Creative Commons licence via OAPEN and HathiTrust as a fully downloadable PDF."
"Textbook Revolution is a student-run site dedicated to increasing the use of free educational materials by teachers and professors. We want to get these materials into classrooms. On this site you'll find links and reviews of textbooks and select educational resources."