Books
📚 OpenStax
A pioneer in liberating higher education, OpenStax offers peer-reviewed, openly licensed college textbooks—covering everything from calculus to classical mechanics—completely free online (and low-cost in print).📖 Wikibooks
Part of the Wikimedia family, Wikibooks empowers learners and teachers to collaboratively create and edit open-content textbooks and manuals across subjects like mathematics, physics, and engineering.🌐 Global Text Project
Dedicated to educational equity, the Global Text Project publishes open-content electronic textbooks aimed at underserved university students in developing countries, all freely downloadable under Creative Commons licenses.📔 Project Gutenberg
The oldest digital library, Project Gutenberg provides over 75,000 public-domain eBooks, from classic physics treatises to fundamental mathematical works, available in EPUB, Kindle, and plain-text formats.🎓 Bookboon
Bookboon offers free textbooks written by professors at leading universities, with concise chapters and practical examples in engineering, IT, business, and more—supported by unobtrusive advertiser sponsorship.🏛 HathiTrust Digital Library
A partnership of research libraries, HathiTrust curates over 18 million digitized items, providing full-text search, downloads, and text-and-data mining tools for both public-domain and copyright-protected works.📚 Bartleby.com
Bartleby.com hosts a wide range of classic reference works, anthologies, and literary collections in full-text, searchable format—ideal for quick access to foundational texts in mathematics and physics.📘 OAPEN (Open Access Publishing in European Networks)
OAPEN provides a quality-controlled library of open-access academic books—primarily in the humanities and social sciences—with full-text PDFs and peer-review standards upheld by European publishers and libraries.📗 DOAB (Directory of Open Access Books)
The Directory of Open Access Books (DOAB) indexes over 89,000 peer-reviewed academic books under open-access licenses, searchable by subject, language, and publisher, all free of charge.📙 Internet Archive
Beyond web archiving, the Internet Archive’s Books & Texts collection offers over 2 million modern books and 20 million total volumes—rare, out-of-print, and historical works available for free borrowing or download.