Ranked in these QuestionsQuestion Ranking
Pro Available in multiple languages
CheckiO crowdsources translations for problems. Currently problems have been translated in 10 languages. So it's highly possible that eventually more languages will be supported.
Pro Community backed solution reviews
Users can publish their solutions for different problems and other users can review the code and give their opinions on how they would have solved the problem.
Sometimes, some of the most active users get their code reviewed by Guido Van Rossum (the creator of the Python language) himself.
Pro Ability to create new challenges
New missions can be created and uploaded using GitHub. After that is done, it's suggested to CheckiO and if it fills all the requirements after being reviewed by a CheckiO team member, it's pulled into the game.
Pro Challenges from GitHub, O'Reilly, Dropbox and Hubspot.
Con Not for absolute beginners
CheckiO does not teach syntax, instead it teaches how to solve problems using a particular programming language therefore some basic programming knowledge is required to start.