The website is free. The courses include some interactions with the teachers but as long as you register during the time they accept registration, the ressource will be accessible forever.
Many popular course are re-run each year or so, evolving and improving. So, you can try to better understand what you didn't get from the previous edition or simply register to the course you miss last time.

The level of the program greatly vary from one MOOC to another. Some advertised to be for 18-year old young student. Some help me complete the program of my master degree.

There is also french course, especially for people who need the vocabular to start living in France or work in French.

Science & Tech
Association for Computer Machinery Digital Library
Light and Matter
O'Reilly Open Books Project. Note on this one, some of the links lead to semi-broken pages, but if you scroll down, the books are broken down into pdfs of each chapter.
OpenBookProject
FreeTechBooks. This one may jump out as fake, but in reality it's a collection of links to original sources of freely distributed books, e.g. A Practical Introduction to Python Programming.

Philosophy
Stanford Encyclopedia of Philosophy

General Info
GCFGlobal

Some open resources shared by @otter@lemmy.ca:

• https://opentextbc.ca/
• https://ubcwiki.ca/academics/classes/textbooks.html#-hall-of-fame
• https://collection.bccampus.ca/

A must in my opinion for self-learners. It also has an Android app: https://f-droid.org/en/packages/com.ichi2.anki/

Building a Study Plan

Gather Your Resources

When trying to teach yourself a topic from internet resources, it is important to understand that you are very much constrained by the resources available to you. Free resources may be difficult to come by or out of date. To that end, an essential first step is to survey what resources are available and compile them into a study plan.

A Note on Study Buddies:
At this step, you may also want to reach out to one or more people you know have a similar interest. Having somebody to go through the process with you can make understanding the content less burdensome, while also improving motivation to learn.

Types of Resources

• Books
• Lectures
• Mnemonic
• Supplementary

Set Goals

Establish time-based milestones that you can use to regularly evaluate your progress. Be realistic and ready to change your plan if you're not meeting those milestones. Remember, because you're only accountable to yourself (or your study group) it's not such a big deal if you miss a deadline. To that end, giving yourself enough time to accomplish the milestone in the first place.

Similarly, you should establish consistent short term goals to maintain motivation and momentum. Things like making sure you consume some amount of learning material every week or ensuring you review your flashcards every other day will make a big difference in ensuring you don't lose track of your learning project.

Taking Efficient Notes for the Long Term

This step is optional but will make a huge difference, particularly in long-term retention. With that in mind, it is important to choose a note-taking method that will last. The first choice to make is digital or paper-based. Digital has the distinct advantage of being searchable and easily backed up, but if you're like me, it can be difficult to keep up with a single digital note-taking system. Paper by contrast has a more timeless quality to it and is far more flexible as far as your ability to record graphs and uncommon symbols (such as in advanced math courses).

This guide is a living document. If you believe something should be added or changed, please make a comment to that effect.

Until this community goes through a round on the new communities/promo communities, you are unlikely to get significant response when posting here. However, I would be very excited to hear ideas about how you think this community should be run and what resources it should offer. Please feel free to post to that effect. Similarly, if you are interested in joining the mod team, please reach out.

The courses are substantially more complete than typical OCW courses and include new custom-created content as well as materials repurposed from MIT classrooms. The materials are also arranged in logical sequences and include multimedia such as video and simulations.