Dolphin Smalltalk is a nice Smalltalk System for Windows. Version 7 will be available today and it will be fully open source with MIT license on GitHub. Read more.
The sources for both the image and the virtual machine will be available.
For those who do not know it:
Dolphin is a Smalltalk system for Windows provided by Andy Bower and Blaire McGlashan from www.object-arts.com. The article from BitwiseMag gives an overview.
The existing Dolphin 6.2 codebase was brought by Andy Bower now under Git and compiles completely under VisualStudio Community 2013.
This is a new version, Dolphin 7, that is modelled off the previous X6.1 Professional Edition (although you can choose to build Dolphin Community
Edition from it if you like).