I recently started using Exercism.io to practice my code skills. I really like Exercism because, unlike other websites focused on practicing on code problems (or katas), you can use your own tools and editor. I'm a huge fan of using Sublime, and I really enjoy it rather than using an editor inside of a website. Exercism allows you to solve problems and have them reviewed by people, so it's a really great way to learn from your peers. There are similar tools to Exercism, but Exercism comes without a price tag. If you feel you've already tackled all of the problems Exercism has to offer for your programming language, you could try out Upcase. I've heard some great things about it as well.