LeetCode - Practice and level up your development skills and prepare for technical interviews.
FaceCode - Hire top tech talent with video interviews
Edabit - Learn to Code in 90 Days or Less
Daily Coding Problem - Get exceptionally good at coding interviews
Codewars - Achieve code mastery through 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.