O'Reilly provides an online library with a huge number of ebooks and video courses in the field of computer science. Their content covers all the major computer science topics, so you will be able to learn about programming languages, platforms, algorithms, AI and more. Most of their content can be accessed via web browsers and dedicated mobile applications - for Android and IOS - and for the mobile apps you can even download content for offline usage.
Normally the subscription costs $499 annually - as per this link at the time of writing - which is a huge number for many people, especially in developing countries. Here I will show you how to get access to most of this content without paying those enormous $499.
ACM - Association for computing machinery - provides access to part of the O'Reilly online learning platform features as part of its subscription. According to the ACM, you will have access to over 40000 online learning artefact as a benefit of your ACM subscription. In my experience, I found almost all the books I searched for that I know exist on O'Reilly online platform.
You can join the ACM through this link. There are two major types of subscriptions one for students and the other for professionals. You can find the detailed comparison between the two subscription types here, but there is no difference regarding accessing the online learning platforms and if you are a student you will enjoy a discounted subscription. At the time of writing the basic professional subscription costs you $99 while the basic student subscription costs $19 only. here you can find prices for all subscription options.
There is also an option to add the ACM digital library to your subscription which will give you access to all ACM papers and books. I didn't try this option myself, so I can't describe it completely.
O'Reilly learning platform is not the only benefit of your ACM subscription. Among other things, you will have access to the Skillsoft platform, which is another online learning platform providing ebooks, video courses, certificate training and trial exams - not the certificate real exams. Like the O'Reilly platform, you can access Skillsoft via web browsers and a dedicated mobile APP, but my experience with their online ebook reader was not good, so you may decide to read Skillsoft books on mobile devices only. I found some books on the Skillsoft platform that I didn't find on O'Reilly, so it's not another redundant subscription.
If you are in a developing country, you can have a discount for the professional subscription. The discount may vary by country, and in my case, the whole annual subscription costs $25. Follow this link for the full list of developing countries. After selecting your country - if it exists in the list - you will go to the subscription forum which has the prices for the different options near its end.
For developed countries citizens if non of the discounts here apply to you, then the only remaining method - as per my knowledge - will be to find some existing ACM member and make him/her referring you. Doing this you will receive an invitation with a discounted price for the first year and he/she may receive some prizes too.