hackattic - No nonsense, real world programming challenges
Real Dev - Real-life coding skill challenge
Code Fight Club - A fight club you can talk about. Less punching, more coding.
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.
Frontloops - Level up your frontend skills with handcrafted tasks