It's easy to forget all of the computing operating systems that existed before Windows, Mac OS, and the various flavors of Unix / Linux. But if you ever feel like taking a walk down memory lane and checking out some screenshots of some of the oldies, check out the Graphical User Interface Gallery over at Guidebook. There are a bunch of beloved bygone GUIs, as well as a few that I had never heard of. What the hell is IRIX or Visi On? It seems the gallery is pretty full-featured, but unfortunately needs some help filling out the galleries on some of the more obscure OSes. It's still well worth a 5 minute perusal.