Squeak.org

Free, open source, open research, super portable, new Smalltalk-80-based language, written in itself, by Smalltalk's inventors, the (nomadic) original Xerox PARC, Alan Kay team, now founding the Viewpoints Research Institute. Runs on 22+ platforms, hardware and OS. "Next to universal access, malleability is the prime figure of merit for Squeak. It is our intention for Squeak to evolve." Now hybridized with the Self language's Morphic User Interface Toolkit.