SimplyGNUStep is now based on Debian Sarge (the upcoming Debian version). So it's simply just a collection of Debian packages with current GNUStep applications. The previous project of the same name aimed to be a full distribution, with its own directory structure, just like NextStep was organized. I find the current incarnation much more sensible though - having yet another package system and yet another distribution doesn't really make sense, especially when Debian already offers everything in very usable form...