Xcode 4 was rewritten completely from scratch and features a significant number of changes from its predecessor, many of which are aimed at improving the workflow that developers use to program apps on the company's two operating systems.

In addition to a completely new UI, Xcode adds official support for the LLVM compiler and code analysis, an advanced technology that makes spotting mistakes in source code easier. The new IDE can even automatically correct some simpler mistakes, thus helping developers write code more efficiently.

The many advances of Xcode 4 come at a price, however--the new tool is a radical departure from its predecessors, both in terms of functionality and user experience. Despite the fact that beta versions of Xcode 4 have been available to registered developers for several months, it's likely that its introduction will cause some confusion among longtime Xcode users who need to get acquainted with the new features.

As has always been the case, Xcode 4 is available as a free download (which also includes the OS X 10.6. and iOS 4.3 Software Development Kits) to registered members of Apple's iOS and Mac Developer Programs.

In another break with tradition, however, the company has chosen to also make the IDE available to the general public through the Mac App Store, where for the modest sum of $5. Xcode 4, which is a hefty 4.24GB download, requires Mac OS X 10.6.6.