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There has been an incredible rise in free online education platforms in recent years, and it is encouraging to see how accessible learning has become. While access to a computer and the Internet is still a requirement, connectivity continues to expand, even in developing regions. Five years ago, the idea of taking a free cryptography course from Stanford would have sounded impossible. Today, it is a reality for anyone with an Internet connection.
Below are a few platforms I have personally used or explored. Each offers high quality courses across a wide range of subjects. Khan Academy remains one of my favorites. It takes a different approach from traditional classroom formats, but the clarity of the instruction is outstanding. The breadth of topics covered is impressive and the teaching style makes even complex subjects easy to understand.
Here are some great places to start:
https://www.udacity.com/
https://www.khanacademy.org/
https://novoed.com/
https://www.coursera.org/
http://online.stanford.edu/courses
Enjoy exploring and learning.