These commands are good as of 2011-07-27.
2014-06-05: update for OSX Yosemite: https://gist.github.com/chrisb/4d6a09c6cc1ca2e1b14e 2013-10-24: update for OSX Mavericks: http://dean.io/setting-up-a-ruby-on-rails-development-environment-on-mavericks/
App store http://itunes.apple.com/us/app/xcode/id448457090?mt=12)