SproutCore began gaining popularity last year when it was revealed that the .Mac Web Gallery was built on top of it. Created by Charles Jolley, the framework differs from other JavaScript libraries like Prototype and Scriptaculous in that it provides hooks for building entire applications, not just doing special effects.
What makes SproutCore so different? Charles explains:
"SproutCore is for applications that want to adopt this new 'thick' client model for building apps on the web. If you are creating static pages with a widget here and there, then SproutCore is probably too much for you and another framework such as YUI, Dojo, or Mootools will do the trick. If you have built desktop applications in the past and you would like to bring that same experience to the web, however, then you will feel right at home with SproutCore."
SproutCore uses Ruby to generate the static HTML and JavaScript files that drive it. This doesn't tie the framework to Ruby, though, because the code it generates runs on the client side. As long as your backend can understand JSON notation, it can communicate with SproutCore whether it was built using Java, C#, or Perl.
Some interesting developments since WWDC (as publicized on the SproutCore blog) include the release of version 0.9.10 of the framework, publication of a bundle for TextMate, and creation of a wiki and Meetup group.
SproutCore is open sourced under the MIT license.