Leetcode
Founded: 2015
Certification Provided? Yes
About: LeetCode is one of the most well-known online judge platforms that you can use to practice your programming skills by solving coding questions. It has over 1,100 different problems, support for over 18 programming languages, and an active community that is always there to help you with the solutions you come up with. If your intention is to hone your coding skills, then this online judge platform is one of the best that you can use.