(I found this on Reddit)

These are the most commonly shared resources. These are the "big four" in my opinion, but they aren't necessarily the best or the most quality. If you're new to online learning, these are the ones you'll probably go to first.

  • EdX. Free courses from top universities, pay for a verified certificate. EdX certificates are probably the most valuable certificates here.

  • Coursera. Free courses from top universities again, pay for a verified certificate. Has more options than EdX.

  • ALISON. Lots of free courses with free certificates. In my opinion these courses are not the best quality but if you want some free certifications quick, it's good for that. I would personally advise against spending money there.

  • Khan Academy. Tons of free courses with tons of useful content, particularly in math. No certificates.

New resources

Here are some rarely-shared resources, and in my opinion they're the most valuable.

  • Freecodecamp. Free courses on web design (300+ hours each) with free certificates. Incredibly streamlined.

  • Aquent Gymnasium. Free courses on web design and related topics with free certificates. Definitely one of the highest-quality providers here.

  • Stanford Lagunita. Free courses on advanced topics from fucking Stanford with free certificates.

  • OpenLearn. Free courses from the Open University, many with free certificates (technically "statements of participation"). Very high-quality courses.

  • proValens Learning. Free and paid courses with certificates from the National Parks Service. I have 3 certificates from here; I highly recommend them if you're interested in this type of stuff.

  • Google Digital Garage Tons of free and paid courses, with a pretty valuable free certificate in digital marketing

  • Saylor Academy. It's been a long time since I used Saylor Academy but last I remember, they offered free courses, with free certificates, and the learning was pretty high-quality. It might have changed in the 6 or 7 years since I've used Saylor. But they're still advertising "Free, Modern Certificates" on their homepage so maybe not.

Misc. resources

Here are some niche resources that don't have such a wide audience or don't offer certificates, but that I have personally found very useful and/or interesting and/or funny.

  • School of Haskell. Learn Haskell for free. No certificates.

  • YaleCourses. Free video courses hosted on YouTube; a ton of really good information here. Of course, no certificates.

  • Hillsdale College. Free courses with free certificates from a real college -- a private, conservative-leaning Christian college that is.

  • Theoretical Minimum. Free courses on advanced science topics lead by a seminal physicist, Leonard Susskind. No certificate but the education is top-notch.

  • Become a certified artist instantly. It's a joke, but hey, free certificate! Remember to get a free randomly-generated artist's statement while you're at it, too.

  • Game Theory Online. Nice little lecture series on game theory that is both standalone on YouTube and hosted on Coursera. It's an okay course but I prefer:

  • Game Theory 101. Actually has a ton of free video courses ranging from logic to international relations. No certificates but full of good, useful, dense information.

  • Open Music Theory. An online course (technically a "hybrid textbook") from Hybrid Pedagogy on, you guessed it, music theory. No certificate.

  • Semiotics Institute Online. Free, highly advanced courses on semiotics led by eminent theorists. No certificates. My personal favorite, but I'm a big nerd and have a background in semiotics already.

  • Catholic Online School. Tons of free course with tons of free certificates...but it's an online Catholic school. I took a course for fun and now I have a certificate in, uh, "Secret Message of Our Lady of Fatima."

  • Wikiversity. Tons of user-made courses and other learning resources. It presents itself as a hybrid between a university and a wiki, it even conducts its own research and publishes its own journals! No certificates of course.

  • Any of the sites listed here. This is a list of websites which use the EdX architecture, so they're essentially clones. There's a ton to go through and only a fraction of them work, and even less are open to the public. Still, there might be some hidden gems here and there. Some of them will provide certificates and others will not.