Squeak is an open, highly-portable Smalltalk-80 implementation whose
virtual machine is written entirely in Smalltalk, making it easy to
debug, analyze, and change; it includes among other things:
    * a rapid-turn-around Smalltalk-80 compiler,
    * a caching-JIT run-time virtual machine (with full source in
      Smalltalk),
    * large class libraries with portable data and GUI models, and
    * an integrated development environment with powerful coding
      tools and GUI construction tools.

Squeak was developed at Apple Labs, Walt Disney and has been ported
to a variety of computers (including most flavors of UNIX and Windows).
Compared to other Smalltalk systems, Squeak has 4 important features:
    * Portability (to Mac, Windows, WinCE, and many flavors of UNIX);
    * Speed (it uses native C for compute-intensive code);
    * Price (free, including all source code and the right to distribute
      applications!); and
    * Sophistication (full Smalltalk-80 language, libraries, and tools).

Squeak comes under an open source license, meaning that you can
download and use it for free.