Project Gutenberg

arXiv is the open-access preprint repository where physicists, mathematicians, and computer scientists publish research papers freely, often months or years before journal publication. It lets anyone read frontier research, including most AI papers, without paywalls or institutional access. Preprints are not always peer reviewed, so reading critically is part of the deal.

The Directory of Open Access Journals indexes roughly twenty thousand peer-reviewed journals whose articles are free to read, acting as a quality filter that screens out predatory publishers. It is the starting point for finding legitimate research without paying journal subscriptions. It indexes journals rather than hosting papers, so you still click through.

The Internet Archive is a nonprofit library preserving the web through the Wayback Machine alongside millions of books, recordings, films, and software programs, all freely accessible. It is civilization's working memory against link rot and platform deletion. It is also a single organization facing lawsuits and outages, so treat it as a resource, not a backup.

OpenStax, based at Rice University, publishes peer-reviewed, openly licensed college textbooks in math, science, economics, and humanities, free to read online or download as PDF. It removes the textbook-pricing gatekeeper from self-education, and open licenses mean the books can be copied and kept forever. Coverage centers on standard introductory courses.