I was recently asked about building projects that use GNUstep from Xcode. The fact is, it’s incredibly easy.
By default, GNUstep on Mac OS X installs its libraries to /usr/local/lib and its frameworks to /Library/Frameworks. Therefore if you want to include GNUstep-base additions, you just hit the + button in your target’s “link binary with libraries” section and find the libgnustep-baseadd.dylib entry under Mac OS X 10.7. If you wanted to use GNUstepWeb, you’d look for WebObjects.framework in the same list.
You can get access to the GNUstep base additions in your code by including <GNUstepBase/GNUStep.h.
Notice that if you manage a GNUstep project using Xcode, you’ll only be able to build it on a Mac (unless you go to the bother of writing a build tool with GNUstep’s unfortunately-named XCode.framework – which ironically doesn’t currently work on Mac OS X.). If you need to target non-Mac platforms, your options are to build Cocotron-style cross-compilers and add them to your Xcode project, or to create an Xcode project with an External Build System target and manage your build via make anyway.
An interesting extension would be to define a new filesystem layout for GNUstep-make that deposited all of the frameworks and libraries into a .sdk folder that could be used in Xcode as an additional SDK.