Real Dev - Real-life coding skill challenge
LeetCode - Practice and level up your development skills and prepare for technical interviews.
hackattic - No nonsense, real world programming challenges
Edabit - Learn to Code in 90 Days or Less
HackerRank - HackerRank is a platform that allows companies to conduct interviews remotely to hire developers and for technical assessment purposes.
Codewars - Achieve code mastery through challenge.