CodinGame - CodinGame provides users with a fun and effective way to learn coding that eschews the rigid structure of traditional teaching methods.

Real Dev - Real-life coding skill challenge

Rosetta Code - Rosetta Code is a programming resource that provides example problems of how to write the same...

hackattic - No nonsense, real world programming challenges

Codingbat - The online programming practice in java and python.

HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.