i'm now considering nodejs, because of the non-threaded but high-performance approach.
Of course it's multiplatform and scriptable.
It would not be a single exe, i know, but it would have many other advantages.
I expect the package to be 2MB zipped and 2-3MB once installed.
The GUI would be actually web based, this would make it available over the net.
A little exe would make the shell integration, run it as a service and provide tray icons.