I used to maintain some slackbuild (
www.slackbuilds.org) scripts for GNUstep a while back but I haven't had Slackware installed on any of my computers for years, now. Building GNUstep for Slackware is really easy since it includes, by default, all required dependencies. GNUstep has one of the easiest build systems out there, but still requires you to compile a big chunk by hand. That sometimes scares people first coming into contact with it. I can tell you it's no big deal.
As mentioned before, Bean for GNUstep is hosted by the GAP project. I used it a few times in the past but I didn't find it "ready for primetime" back then.