"Xcode, Apple's tool suite and integrated development environment (IDE), is the fast and easy way for developers to create applications for Mac OS X Tiger.
Xcode is designed to let you take advantage of all the great technologies that ship in Mac OS X. In addition, you can ensure that your application is ready for the future: starting with the current version, Xcode 2.1, you can build a universal binary application that runs both on current PowerPC-based Macs and the upcoming Intel-based Macs. Developing with Xcode helps you create great applications now, and brings you well along the path to the future."
I've yet to use Xcode, even though I've been meaning to. I'm more of a texteditor/comand line kind of person.