From their site.
What is it?
GNUstep (this is a live CD, an operating system, a distribution) contains a lot of software for GNUstep, a free implementation of the OPENSTEP framework (which was also the base as Cocoa in Mac OS X). It includes an excellent application called Gorm for RAD (Apple Software Design Guidelines).
The GNUstep LiveCD is an excellent tool for testing out your PowerPC hardware for compatibility with linux. As for installing GNUstep, well one needs to install debian first then "apt-get install gnustep gnustep-devel gnustep-games wdm menu" for GNUstep.