UX Challenges - Done reading about UX? Start doing it.
UXCurate - Practice whiteboard challenges and get feedback 👨🎨🎨
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.
skribbl - Word guessing based on drawing.