Xcode is an Integrated Development Environment (IDE) containing a suite of software development tools developed by Apple for developing software for OS X and iOS. First released in 2003, the latest stable release is version 4.5.2 and is available via the Mac App Store free of charge for Mac OS X Lion and OS X Mountain Lion users. Registered developers can download preview releases and previous versions of the suite through the Apple Developer website.
Read more about Xcode: Composition, Toolchain Versions, Major Features