Open courses, free textbooks and study tools that cost nothing
Free and free-with-conditions are different things, and a lot of students waste a term working that out. Everything here is genuinely open: no institutional login, no geographic restriction, nothing that stops working the day you graduate.
How I use them: one of the big free course platforms when a prerequisite did not stick the first time and I need a topic taught again slowly; open courseware from a major university when I want to see how a hard subject is taught at depth, problem sets included; open textbook libraries when the assigned textbook costs more than a week of food, which is most semesters. Literature and history students get a lot out of the public book archives, where out-of-copyright classics are permanently free to read and many other books can be borrowed for a fortnight at a time.
One honest limitation: these resources are strong on fundamentals and weaker on whatever your specific lecturer cares about. Use them for the concepts, and your own course material for the exam. Quality also varies, because anyone can contribute to some of these platforms, so prefer the ones with institutional backing when you have the choice. And if you find yourself about to pay for something, check the student perk page first - a surprising number of paid platforms hand students their top tier for nothing.
Khan Academy is the first place I send any student who says 'I don't get this.' The lessons are broken into 5-15 minute videos with practice problems right after, so you can actually finish a topic in one sitting. Used it to claw back a C in stats the semester I stopped attending lecture.
MIT OpenCourseWare hands you the actual lecture notes, problem sets and exams from real MIT classes - for free, with no signup. It is the single best free resource on the internet if you are self-teaching a hard subject. Not for the faint of heart though: the problem sets are brutal.
OpenStax publishes free, peer-reviewed textbooks used at hundreds of US colleges - biology, psych, econ, calc, the usual gen-ed lineup. Saved me around $400 a semester when I switched from the campus bookstore. The PDFs are clean and the online reader works fine on a phone.
Project Gutenberg is a 70,000-book library of public-domain works, free in any format you want - Kindle, EPUB, plain text. Lifesaver for English lit classes where the assigned edition costs $25. Skews heavily toward older works, so don't expect to find modern novels here.
Google Scholar is the search engine every college paper actually starts from. It indexes peer-reviewed papers, theses, books and abstracts, and links to free full-text versions when they exist. Saved me dozens of times on lit reviews - paste a citation into 'Cited by' to find the newer papers that reference it.
The move nobody tells you: hit 'Audit the course' and you get the full lectures and readings from Yale, Stanford, Michigan - free. No certificate, but the knowledge is identical. I audited an entire machine learning specialization the summer before taking the actual class and walked in already knowing the first month's material.
edX is where I took Harvard's CS50 without paying a cent or leaving my bed - full lectures, problem sets with automated graders, and a real final project. The audit track is free forever (just no certificate). CS50 alone justifies this whole list; it's the best-taught course I've ever experienced, and it costs nothing.
freeCodeCamp took me from 'what is HTML' to shipping a real web project without me spending a dollar - the entire platform is a nonprofit with no premium tier lurking. The certifications (responsive web design, JavaScript, Python) are respected enough to put on a student resume. Their 4-hour YouTube deep dives carried my database class.
LibreTexts saved me when my chemistry professor assigned a $180 textbook that we barely used. It is the largest open textbook library on the web - full, real textbooks for chem, bio, physics, math, engineering and more, organized by course. The worked examples in the chemistry library are genuinely better than my assigned book.
Open Library (run by the Internet Archive) is my first stop before buying any book. Millions of titles are readable or borrowable for free, and out-of-copyright classics like Frankenstein or Dracula are permanently free to read online. For literature courses it replaces half the reading list.