Hi! I'm new here. My name is Stefano and I am from Italy :-)
SymbOS (www.symbos.de) is a "Windows like" operating system for Z80 computers (Cpc and Msx for now) and it is possible to port it in Zx +3. I think is possible also to run it in Pentagon, Scorpion, Atm Turbo and Sprinter.
Features: REAL MULTITASKING * 576KB DYNAMIC MEMORY *
* 128GB FILESYSTEM * 100% WINDOWS GUI. I have written to author and he wrote to me is possible to port it on Zx +3 (only +3 'cause limitation with ram pages). It is necessary to modify code you can find here: http://www.symbos.de/download.htm. It is incredible! See the amazing video here: http://www.symbos.de/videos/trexsymbos1.zip
This is reply to the email to the author of the project:
Sorry for this very late answer, somehow your email got lost first. Thanx for your interest in SymbOS. I think a Spectrum port would only be possible for the Spectrum +3 because of the memory bank switching requirements. Even the Sam Coupe wont be able to handle it completely because of its 32k block limitation.
On the other hand I wonder if a new memory expansion would be possible for all Spectrums, which is able to provide the required bank switching possibilities.
The memory is always the most important thing for a port (beside the Cpu of course ;-).
But Doors is already a very great Windows OS and it is perfectly designed for the Spectrum graphic. So I am not sure, if SymbOS would make sense?