Real Dev - Real-life coding skill challenge
hackattic - No nonsense, real world programming challenges
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.
AlgoExpert.io - A better way to prep for tech interviews
Takehome - Effective and humane coding challenges for candidates