I admit that I haven't personally used Darling but it would be rather pointless if it only worked for commander line apps. All command line apps I use on MacOs X are from homebrew and are available in Linux so for me it only makes sense for GUI apps. Also, I never really missed a MacOs X specific app when I use Linux, most apps I use are multi platform anyway, and the rare one that is not, it usually has a decent equivalent for Linux.