Several collegues have directed my attention to an interesting website
Operating System Interface Design Between 1981-2009. The website comprises a fine range of systems, and not only lists well-known systems like Xerox Star, Lisa, Mac, Amiga Workbench, and Windows, buts also less known ones like GEM, KDE, and GNOME. Regarding user interfaces, the website presents fine screenshots from all the systems. I find that the term Operating Systems is a bit misleading as the paper does not present the command line interfaces of UNIX, LINUX, etc. So I suggest you think of the site as a GUI history site.
