reverse cygwin

Cygwin presents a unix/linix API so that unix/linux apps can be ported
to run under windows. Is there a package that does it the other way
around, that is a Windows API under unix/linux that allows Windoze apps
to be ported to unix/linux? I have used vmware, but I was looking for a
porting environment rather than an emulation thing.

Thanks,

-Doug