I messed around with GNUstep on Ubuntu around 2011-ish when I tried to port an OS X service to Linux. (I did not touch Etoile, though, as I didn't need a GUI.)

I messed around with GNUstep on Ubuntu around 2011-ish when I tried to port an OS X service to Linux. (I did not touch Etoile, though, as I didn't need a GUI.) I didn't come away with a good impression at all. It was not very easy to get up and running, the documentation was lacking, requiring digging through many mailing lists, and it didn't support Objective-C 2.0... which was a big pain since the code was in Objective-C 2.0. Some of the libraries didn't even compile, for which I submitted a patch or two that never got accepted. When I finally got the app to compile, it was rather slow, so I abandoned further work. Looking at the wiki, it apparently still does not properly support Objective C 2.0, and does not even mention plans for things like ARC. I don't think it'll see any adoption until they bring it closer to modern Objective-C style development.