So am I understanding this correctly, but this is not a compatibility layer where we can run native linux applications on windows, instead it's like cygwin where we can run ported applications, only this one uses pacman for distribution of packages?
Some of the software is Cygwin-like, but not much, only enough to distribute (and build) the native (mingw-w64) software and provide a shell.
There was LINE which was superceded by CoLinux. However the 64 bit port of CoLinux was never completed.