Squeak - powerful Smalltalk programming language

Squeak is a modern, open source, full-featured implementation of the powerful Smalltalk programming language and environment. Squeak is highly-portable - even its virtual machine is written entirely in Smalltalk making it easy to debug, analyze, and change. Squeak is the vehicle for a wide range of projects from multimedia applications, educational platforms to commercial web application development.

Squeak itself is an IDE. You can code, run and debug in the same environment. It supports Unicode and Localization for multi-lingual applications.