PHP can in principle be used to create applications that are not web based. When you install PHP on a Linux system you can run any PHP script just by typing
The output is then written to the console. I sometimes use this for debugging purposes.
PHP can even be compiled with bindings to libraries like NCurses or Newt, which allow to create a simple user interface.
Yes, it can be used for that, I made console-based servers and clients (using socket programming) in php under linux. And that's not all, ot has an extension for gtk+ which enables you to actually create windows under Linux (I didn't try this... yet ) and it has a win32 extension which enables you to create windows under Windows (didn't try this either :P)...