I am putting together a list of websites that can be used to learn / teach / practice coding — or more broadly computer science concepts — with a hands-on approach. Do you have any suggestions?

The goal of this is to find the best websites that can be used to help provide resources to middle / high school students who may have access to a computer, but can't afford to own one themselves.

My main interest is to find sites that are free, approachable, allow someone to create an account to store work / keep track of progress. The site also doesn't necessarily have to use a standard programming language. All alternatives welcome!

So far I have focused on sites that tend towards graphics, since that may be a compelling hook for younger students, but would love to hear as many suggestions as possible. Thanks!

Some example sites:

https://www.shadertoy.com

http://glslsandbox.com

https://www.codecademy.com/learn

https://www.openprocessing.org

http://codepen.io