You know how Apple is famed for their wonderful UI design? Well, they don't always hit the nail on the head, it would seem. From the iPhone SDK installer:
Yargh! In fact, it really means that it is installing MacOS 10.5 development tools, but it is one scary way to put it.
In fairness, though, the new version of XCode is quite the prettiest IDE I have ever used. You should see the code completion! And as for the electric brackets... stunning, simply stunning. Brings a tear to the eye.
Sadly, I do most of my proper work in Eclipse (CUSP and ErlIDE), which isn't so pretty.