Their engine supports many languages including less common like Haskell Bash Groovy Golang Rust Scala and they can be used to solve all the challenges available on the site. A large part of the community is French speaking and it exists a French version of the site.
It has helped me learn new languages in the best possible way: By building AI's and playing games! No weird challenges in which you have to have some specific knowledge to solve. Just use your brain, research the solution that best fits your approach and apply it against other players. For me, it's the best!
It's impossible to copy and paste to/from the site. I suspect this is on purpose, because any reasonable code editor would have this feature, and you'd have to go to a great extent to break it.
Working with your own IDE is impossible: when you select something into the site, it deselects your text quite quickly, though it is possible to select.When you paste something, it progressively indents the text (at least with Python). This was not even disabled for the tutorial.
I thank AlternativeTo for existing, because they allowed me to find alternatives to this poor user experience. I will try some of them out; I'll probably pass on CodinGame's opportunity because of this copy/paste conundrum; as much as its gamification tries to hook me into addiction. The same happened to me on HackerRank.
I think any site messing with your browser's basic functions infringes upon your right to use your computer. (Richard Stallman, founder of GNU, noticed that if you can't use the software, then the software is using you.)
The fact that they are doing it for copy protection or enforcing honesty among players is not an excuse. Malevolent people will circumvent the JS, but honest people are repelled by such mistreatment.
[Edited by danhaiduc, September 07]
Our users have written 3 comments and reviews about CodinGame, and it has gotten 30 likes