JetBrains has released AppCode, an IDE for Objective-C that looks and feels similar to their namesake IntelliJ IDEA editor for Java.
The similarities with IDEA will be noticed by those who are familiar with it on other platforms. That includes the fact that the runtime is entirely implemented in Java, which implies that a JVM (1.6 or above) is required in order to run the IDE. On Lion, if a JVM isn't installed then Lion will prompt to download the latest JVM before the app launches; other installs of OSX will already have a JVM installed by default.
As with any IDE, getting used to the way the app navigates presents a one-time learning exercise. Those with long experience with Xcode (and ProjectBuilder before it) are likely to take some time in getting used to the way it works, but those with existing IntelliJ experience will get used to it much faster. The integration with version control systems includes all the popular ones (Git, Subversion, Mercurial) as well as some archaic ones (CVS).
AppCode can open Xcode projects, and although it has no replacement for Interface Builder, it can launch nibs and xibs to bring them up in the already installed version. In addition, for iOS development, AppCode can launch the Apple Developer Tools simulator.
The code detection can look for missing retains/releases, as well as prompt for their inclusion, but it also supports GC and ARC from recent iOS builds. Code smells are highlighted and can be fixed with one of the quick-fix options, or refactored using the same kinds of refactoring available to other JetBrains IDEs.
Finally, testing with AppCode is much easier than it is with Xcode, with an integrated OCUnit runner. Unlike Xcode, which attempts to treat tests as a build-time operation, Xcode can launch tests and debug them within the IDE, including debugging variables during the testing process.
AppCode is available for Mac OS X 10.5 and above, and requires that a JVM and the Apple Developer tools are installed as well. It is available as a 30-day trial and has discounted licensing available until December 31st 2011. It is also available for free for educational institutions and companies, and for open-source project development. http://www.jetbrains.com/objc/buy/license-matrix.jsp