Codewars - Achieve code mastery through challenge.
HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.
edX - Best Courses. Top Institutions. Learn anytime, anywhere.
iMocha - Make intelligent talent decisions.
Treehouse - Treehouse is an award-winning online platform that teaches people how to code.
Codility - Codility provides a SaaS platform with advanced validation, security and protection features to evaluate the skills of software engineers.