UX Challenges - Done reading about UX? Start doing it.
Frontend Mentor - Supercharge your front-end skills by building in a real-life workflow. Solve real-world HTML, CSS and JavaScript challenges whilst working to professional quality designs.
Uxcel - The easiest way to learn UX/UI design
A Product Design Challenge - Get a design challenge to solve real-world problems
uxtoast: Learn UX Design - Become familiar with design laws and learn how to use them.
Singscope - See your pitch analyzed as you sing