From a session detail of this year’s WWDC:
Discover why Mac OS X is the dream development platform for Ruby on Rails, a powerful and agile web development framework that comes bundled with Mac OS X Leopard. By combining Xcode with the power of Ruby on Rails, you’ll learn how to create unified, first-class web applications that are simple to deploy on Mac OS X Server and that display and perform exceptionally in Safari on Mac OS X, Windows, and iPhone.