The list below describes the requirements for developing an application with MacRuby.
You can install Xcode from the Mac App Store. Launch the Mac App Store application. After that, type "Xcode" in the search field on top right corner.
Xcode will appear in the search results. Click on the button to install it.
If you run OSX 10.6.8, Xcode 4.2.x will be installed. And if you use Mac OS X 10.7.x, Xcode 4.3.x will be installed.
If you had previously installed an older version of Xcode (such as 4.2.x) and just installed 4.3, we recommend that you run the following command in the Terminal.
$ sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer/
Since Xcode 4.3, command line tools (such as the compiler, etc) are shipped as part of an additional package. You should install this package.
Next step, we install MacRuby.
The latest version of MacRuby is 0.12. However, and unfortunately, support for Xcode 4.3 has not been integrated in a release yet. Therefore, you must install one of the nightly builds from http://macruby.jp/files/nightlies/. Nightly builds always have latest changes.
IMPORTANT: If you replace Xcode.app (update Xcode.app via Mac App Store), need to reinstall MacRuby.
** OS X 10.6.8 users (only)** will have to install BridgeSupport Preview 3. BridgeSupport is used to get information about the public frameworks APIs of OSX. In OSX 10.7, it is already pre-installed. You can get BridgeSupport Preview 3 from http://macruby.jp/files/, download the BridgeSupport Preview 3.zip file.