What software Puppy comes with varies a bit by release. All versions come with a standard GUI web browser. The current default is SeaMonkey. You can easily download Firefox, Opera, Galeon, and/or others from Puppy's free software repository. (sorry, IE not available!

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Puppy's default GUI is JWM. You can download many others from the free software repository. Icewm and Xfce are probably the most popular alternatives. You could download and install Gnome or KDE but Puppy users generally don't like these resource-hungry hippos.
Bottom line-- Puppy is not much different from other Linuxes in its GUI and interface.