MacRuby is a version of Ruby 1.9 being developed by Apple that allows easy bridging with the Objective-C libraries on Mac OS X, and also compiles Ruby code for greater efficiency and ease of packaging. I recently installed the MacRuby framework and tools (0.4, since I don't have 10.6 so I can't install 0.5b2 yet). It's pretty neat. I like the idea of being able to writing large, compiled Mac OS X apps in Ruby.