It will run on other Linux windowing systems given Qt is installed, but I personally think these are the three platforms on which Qt applications integrate best. It uses the Qt SDK so your code should be cross-platform among Windows, KDE, and OS X.
Qt Creator is an IDE, yet it's very lightweight and quite simple at first-glance. On the GUI text-editing scene on the Mac these are the dominating giants.
Of course, I heard there's also Emacs on OS X, if that's your sex-appeal, or TextMate. If you're the 'flee market' kind of person (like me!) then MacVim with make (or any other build tool) and other tools is your thing.Xcode is to OS X what Visual Studio is to Windows. If you're the 'full-blown IDE kind-of-person' then Xcode is the way to go.
