Pharo is a pure object-oriented programming language and a powerful environment, focused on simplicity and immediate feedback:

• Simple & powerful language: No constructors, no types declaration, no interfaces, no primitive types. Yet a powerful and elegant language with a full syntax fitting in one postcard! Pharo is objects and messages all the way down.

• Live, immersive environment: Immediate feedback at any moment of your development: Developing, testing, debugging. Even in production environments, you will never be stuck in compiling and deploying steps again!

• Amazing debugging experience: The Pharo environment includes a debugger unlike anything you've seen before. It allows you to step through code, restart the execution of methods, create methods on the fly, and much more!

• Pharo is made by an incredible community, with more than 100 contributors (among them the Inria researcht team RMoD) for the last revision of the platform. Hundreds of people contributing constantly with frameworks and libraries.

More infos at http://pharo.org