3.0 Release Notes

@MikDiet кажется еще в третих

But seriously now, it’s really good stuff. There are all the good ideas brought over from when the Merb team joined the party and brought a focus on framework agnosticism, slimmer and faster internals, and a handful of tasty APIs. If you’re coming to Rails 3.0 from Merb 1.x, you should recognize lots. If you’re coming from Rails 2.x, you’re going to love it too.

Full article: http://guides.rubyonrails.org/3_0_release_notes.html