Codeasy is probably the newest one from the whole list. It is quite interesting educational course because it drives a new concept to computer science studying. You start learning there by reading an adventure story about fighting machines in the future. On your way, you’ll meet challenges that require real coding to solve. The final goal is to save the world from machine invasion. And as a very important side effect – become a software developer.

When you reverse-engineer someone else’s code, testing each line to see how it works, you get a better understanding of the big picture. Thanks to the tons and tons of open-source code that’s out there, you can learn just about anything by examining someone else’s (flawless) work. Just remember to share your code back with the community if inspiration strikes and you improve a part of the program you were fiddling with.
EdX is another leading online-learning platform that is open source instead of for-profit. It was founded by Harvard University and MIT in 2012, so you know that you’ll learn about cutting-edge technologies and theories. Today, edX includes 53 schools. You probably can’t go wrong with the free Introduction to Computer Science from Harvard University.
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