hackattic - No nonsense, real world programming challenges
Daily Coding Problem - Get exceptionally good at coding interviews
Codewars - Achieve code mastery through challenge.
FaceCode - Hire top tech talent with video interviews
Real Dev - Real-life coding skill challenge
HackerEarth - HackerEarth is the network of top developers across the world. They connect to start-ups, tech companies, organizations and discover the best developer jobs. They participate in programming challenges and compete against other top developers.