Although, important to note that while Xerox invented GUIs, they were about to trash the project before Apple stepped in and nurtured it. Speculation about what would have happened if they didn't do this is mostly meaningless, but disregarding the promulgation and popularization of GUIs in lieu of crediting only their original inventor is totally unfair.
Actually, Xerox invented some important technologies, such as the mouse and the idea of a windowed interface, but this was not the GUI. That was invented by Apple. The xerox interface was more akin to emacs multi-document mode, there was no desktop metaphor, no file/folders organization, no trash can, the menubar was a very different conceptualization, etc.
