CodinGame - CodinGame provides users with a fun and effective way to learn coding that eschews the rigid structure of traditional teaching methods.
Codecademy - Learn the technical skills you need for the job you want. As leaders in online education and learning to code, we’ve taught over 45 million people using a tested curriculum and an interactive learning environment.
LeetCode - Practice and level up your development skills and prepare for technical interviews.
Codility.com - The programmer testing solution that matches your job descriptions and helps you hire great...
HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.
exercism - Download and solve practice problems in over 30 different languages.