Boris Shingarov's work on Squeak extends in many dimensions:
Porting the VM to OS/2
See SqueakPorts
Porting the VM to large S/390 mainframes
No working code yet.
DLL callout support
He was the first person to make Squeak call outside DLLs. His approach is like that behind PlatformFunction in IBM Smalltalk. The latest archive for 1.30 is Cheese-1.3-v1-os2.zip at ftp://ftp.create.ucsb.edu/
Native Windows: The CHEESE project
He was the first person to make Squeak paint a native OS window. Today, Cheese is at Alpha 59. That's fully functional code for OS/2. Work is being done to port to other platforms.
The last version image: 5.59: http://members.xoom.com/usib6tfj/squeak/cheese59.zip.