Etoys

Etoys is an educational tool for teaching children powerful ideas in compelling ways. Etoys is a child-friendly computer environment and object-oriented prototype-based programming language for use in education.. Etoys is a media-rich authoring environment with a scripted object model for many different objects that runs on different platforms and is free and open source.

Children use Etoys to make their own models, stories, and games, which keeps them engaged because it's a lot of fun. But Etoys isn't just child's play. It's a highly effective way to teach math, science, and language arts, although many children won't realize this. Instead they'll stay immersed in discovery, reaching eagerly for each new idea, making their lessons more meaningful than with a "face-front" approach.

Etoys is written in Squeak (A Smalltalk dialect / sub-language)