Codewars is a platform that helps you learn, train, and improve your coding skills by solving programming tasks of many types and difficulty levels. You choose how you would like to learn. Do you want to take on increasingly difficult challenges? Maybe you prefer training through repetition and by improving your solutions. After solving a task, compare your answer with other users and learn from them or help less experienced users by answering their questions.
codewars.com
A code kata is an exercise in programming which helps programmers hone their skills through practice and repetition. In 1999, the term was used by Dave Thomas, co-author of the book The Pragmatic Programmer, in a bow to the Japanese concept of kata in the martial arts. The concept was implemented by Laurent Bossavit and Emmanuel Gaillot who talked about it at XP2005 in Sheffield. Following this conference, Robert C. Martin described the concept and initial usages in his article "The Programming Dojo".