Emulation Layers: Wine and Linuxulator
One of the things you must admire about UNIX ever since GNU steered into its vanguard is that it tries hard to be complete and inter-operable. UNIX as the operating system is always the hub. But there are important spokes that connect it in a variety of ways to the user. Users of Cygwin/Babun would recognize how important those tools are for Windows users in need of a programmable environment which is so sorely missing in Microsoft platforms.