Not sure about GNUstep, but Darling is akin to Wine, in that it is a re-implementation of the Mac APIs within a Linux environment, allowing you to run MacOS app

Not sure about GNUstep, but Darling is akin to Wine, in that it is a re-implementation of the Mac APIs within a Linux environment, allowing you to run MacOS apps on Linux without recompilation. Whereas Airyx is a full FreeBSD OS (distribution?) that tries to mimic MacOS as a whole.