A closer look at some of Apple's latest software releases shows another dynamic language: Ruby. The most obvious is MacRuby, the Ruby 1.9 port for MacOS X, which leverages Objective-C's mature runtime and GC and allows easy integration with the Objective-C based Cocoa.
Another example is the iPhone Configuration Web Utility - a tool for the Enterprise use of the iPhone, which allows to manage iPhones in a company. A closer look at the Configuration Utility's user guide shows that it's written using Ruby on Rails (from the user guide):
installpath/vendor/rails/railties/lib/commands/servers/mongrel.rb
The tool uses Mongrel on MacOS X and Webrick on Windows.
SproutCore is the toolkit Apple uses for the client side of it's MobileMe applications. While the body of Sproutcore is Javascript that is run in the browser, it's toolset is built with Ruby. The first clue comes from the download/installation instructions for Sproutcore:
sudo gem install sproutcore
SproutCore is installed as a Ruby Gem for a reason: it comes with a toolset to get developers started with developing applications. Developer with Rails or other Ruby frameworks will recognize the concepts. A new SproutCore project is created with
sproutcore app_name
The generated project contains a directory layout set up with necessary libraries and a skeleton application ready to run. SproutCore also uses Generators, written in Ruby, to create models and other aspects of the SproutCore application. Generation of HTML artifacts is done using Merb. To run a SproutCore app during development, either Mongrel or Thin are used to serve the content.
Finally, not an Apple project, but useful for Ruby developers working with Objective-C: Dr Nic shows how to test Objective-C applications (also for the iPhone) using Ruby.