I find Cosmopolitan  fascinating, and this one piece caught my attention:
In order to get programs like GNU Make and Emacs to work on Windows, we implemented new libraries for POSIX signals emulation. Cosmopolitan is now able to preempt i/o and deliver asynchronous signals on Windows, using a SetThreadContext() trick I learned from the Go developers.
Maybe these could help windows porting efforts?
edit: not neccessarily as dependencies, but as examples how such things could be implemented in a portable way.