Difference between iPhone development and Mac OSX development

This question is for all the programmers who code in iphone as well as the Mac OSX platform.

I have been searching on Google for quite some time, but I could not find any good answer, and so I am posting the question here. Please apologize if this is not a programming question.

1. Question on development overview:

   I would like to know how the iphone development tools are different from Mac OSX development tools.

2. Question on the programming language:

   Is the programming done in objective-c for mac-osx as well ? Will it be the same syntax and format (for example, to create a button or textField)... ?

3. Question on the libraries:

   If the programming is done in Xcode, how will the classes and libraries for touch and navigation be for the development in Mac OSX. ? And is there an interface builder ?

4. Question on Simulation and Testing:

   Is it as easy as iPhone development to simulate and test the app in a Simulator ?