Personally I like to watch Youtube videos to learn new and interesting skills. 

https://www.kaggle.com/learn/overview Kaggle offers all kinds of computer science courses.

https://www.khanacademy.org Khan offers classes on all kinds of subjects

https://alison.com/courses Alison also offers a broad spectrum of classes.

I found this while digging around for resources also. https://www.lifehack.org/articles/money/25-killer-sites-for-free-online-education.html