I have been "taking" the MIT 6.824 (6.5840) distributed systems course, and the course is insanely good. (it is not in this article because this is a very advanced CS course.) You can get all the lectures including guest lectures on Youtube, you get labs with TEST SUITES, you get all the Q&As, you get exam questions AND answers. All for FREE. Perhaps the only thing missing from what an enrolled student would get is TA answering questions and discussing with other students or working on projects (and of course MIT credits), which is not too important for me. As someone without a CS background, the course is extremely helpful in getting into dist system.
All the material except video is hosted on their website. No registration or anything. You run the test suites locally to verify that you correctly completed the assignments. It makes you wonder what happened to Coursera, Udacity and many other MOOC projects that were very optimistic and enthusiastic but got worse and disappointing in recent years. This is how it should be done.