It seems that AT&T have a opensource Unix Posix environment for Windows called UWIN
The makers of SFU (Services For Unix) Interop Systems have a vast set of native ports called the Unix Tool Warehouse
Cygwin alternative UNXutils
I’ve never been fond of cygwin, I find it a extremely poor permforming environment, UNXutils suite offers native Win32 binaries of GNU utils 🙂