Articles
Includes various writings and resources.
Better Explained
A site maintained by Kalid Azad that focuses on explaining mathematical concepts as humanly as possible. You could visit the YouTube channel but it's kinda empty of content at this point.
Brain Pickings
It's about whatever your brain might be piqued to.
Explain That Stuff
A series of explainer article of science and technology topics.
GeeksforGeeks
A computer science portal (for geeks).
Personal comment:
Recommend as a referential material.
Medium
A publication platform. This is where most of the tech organizations articles such as from freeCodeCamp and HackerNoon are published. Also, you do have to mind the number of articles you've been reading every month since it is limited for non-members.
Personal comment:
A part of me just wishes for them to create their own article publication platform. \sigh**
Preadr
An article aggregator aggregating articles related to your configured interests.
Scratch A Pixel
A list of articles on computer graphics.
Wikipedia
If you want to learn random things.
Personal comment:
My personal recommendation for mathematical resources. It's seriously one of the best math explainer sites that I've ever seen. To top it all, he also offers a book on calculus that you can read for free in the web.