Xcode 4, released in June 2011, is Apple's integrated development environment (IDE) for Mac OS X and iOS. This tag should only be used for questions about this specific version of Xcode, and not for general Mac or iOS programming topics. Use [cocoa] for Mac programming questions, or [cocoa-touch] for iOS (formerly iPhone OS) programming questions.
Xcode 4 is the successor to Xcode 3, the main development tool for developing software under Mac OS X, targeting Mac OS and iOS. It was introduced to the developer community at Apple WWDC 2010, and the final release was published in March 2011. It was replaced by Xcode 5 in September 2013.
References
See xcode for more information.