How it works: Like buttah. Ruby, the language that powers RoR, has actually been built-in to OS X for a while (don't believe me? type "irb" in your terminal right now to access interactive Ruby), but Ruby on Rails has been mostly a pain to install around OS X. Packages need to be downloaded, settings need to be tweaked, and servers need to be config'd. No more. Ruby on Rails, free and installed on every new Mac. Developers, start your developing.
Who will use it: Mostly people who develop applications for the web. But even though I personally don't code much, if you've ever done any coding, once you dive into Ruby and RoR, you'll probably have the same reaction that I do: wow this thing is neat! For a start in Ruby, check out the classic Why's Poignant Guide, and for a tutorial on RoR, hit up Curt Hibbs (he's from St. Louis, so you know he's a good guy).
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