The MIT Press is committed to re-imagining what a university press can be. Known for iconic design, rigorous scholarship, and creative technology, the Press advances knowledge by publishing significant works by pioneering international authors. The MIT Press is the only university press in the United States whose list is based in science and technology. This does not mean that science and technology are all we publish, but it does mean that we are committed to the edges and frontiers of the world—to exploring new fields and new modes of inquiry. We publish over 220 new books a year and over 30 journals. We are a major publishing presence in fields as diverse as art, architecture, economics, cognitive science, game studies and computer science to name just a few."

This is an easier-to-get archive of all of that project's texts at the Internet Archive.

LibreTexts is the adaptable, user-friendly open education resource platform that educators trust for creating, customizing, and sharing accessible, interactive textbooks, adaptive homework, and ancillary materials. We collaborate with individuals and organizations to champion open education initiatives, support institutional publishing programs, drive curriculum development projects, and more.

LibreTexts is the largest centralized open education project and platform online. Founded in 2008 at the University of California, Davis as the ChemWiki, 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.

This is a curated list of free courses from reputable universities like MIT, Stanford, and Princeton that satisfy the same requirements as an undergraduate Computer Science degree, minus general education.

Textbooks in the Open Textbook Library are considered open because they are free to use and distribute, and are licensed to be freely adapted or changed with proper attribution. The criteria for including new textbooks in the Open Textbook Library are:

• All content must be openly licensed. We accept textbooks licensed with GNU and Creative Commons (CC) licenses, with the exception of the CC ND (No Derivatives) component. CC BY is recommended. Go to Creative Commons for more information about selecting a license for your work.
• Must be a complete textbook available as a complete portable file (e.g. PDF, EPUB).
• Must be in use at multiple higher education institutions, or affiliated with a higher education institution, scholarly society, or professional organization.
• Must be an original textbook (not a derivative of another textbook). Possible exceptions to this criteria are modifications that reflect the needs or context of an entirely new audience. For example, the textbook has been changed in such a significant way that it is now relevant to a new country, profession, or has been translated into a new language. Authors or publishers will be asked to demonstrate significant changes to the original text.

A search engine which indexes where you can purchase over 150 million rare, out of print, new, used, and import-only books online.

A grassroots peer-based education project based around online learning and remote collaboration between small groups of students. They just started up so things are a little thin at the moment. This is an interesting experiment to keep your eye on. Creative Commons.