Edabit is a programming tutorial site that goes beyond teaching basic syntax, and focuses problem-solving skills and how to "think like a programmer." Instead of just showing beginners how to code and stopping after basic syntax, Edabit encourages users to actually make stuff.
Superpowers is an HTML5 development environment for making 2D and 3D games. It can be extended with plugins and lets you collaborate in real-time.
Alice is software that was created at Carnegie Mellon University, and is designed to teach junior high school and high school students computer programming in a 3d environment. Create animations, interactive games, videos, and share them.