Learney - Knowledge aggregator for developers
SnakeLogic - The puzzle based snake game
Multiplication Kingdom - Learn the times tables by playing and having fun in the Multiplication Kingdom (for kids and adults!)
Gumroad Small Product Lab - Bite-sized lessons to help you launch your product.
Khan Academy - Khan Academy offers online tools to help students learn about a variety of important school subjects. Tools include videos, practice exercises, and materials for instructors. Read more about Khan Academy.
Productbox - Talk with fellow product managers about how you do stuff.