The one cross-platform app I know that uses GNUstep to run on Linux is Hopper, which just uses Apple's libraries on Mac. Not sure how hard the porting effort wa

The one cross-platform app I know that uses GNUstep to run on Linux is Hopper, which just uses Apple's libraries on Mac. Not sure how hard the porting effort was, but I thought I'd throw that anecdote in there. As for wine, it's worth pointing out that wine consists of both the plumbing to get win32 apps running on Linux as well as a recreation of the win32 userland libraries. Darling is similar, and it uses GNUstep for some of its userland recreation. Ideally, GNUstep should be a drop in, source compatible framework to compile code written for the native ones on MacOS, similar to how Wine can be a source compatible framework for Windows. There are actually Wine ports to CPU architectures like 64 bit PowerPC that never had native windows versions, and Wine lets you recompile and run win32 software on ppc64le. (Of course, the practical caveat is GNUstep isn't implementing OS X's API, but OpenSTEP, which OS X/MacOS still mostly (?) implements as a subset of its current API. So, if you wanted to be cross platform and use GNUstep, you'd either need to develop on Linux, link against GNUstep on MacOS, or be super familiar with MacOS to know what APIs are available on both)