sproutcore seems to be a new kid on the JavaScript framework block with lots of ambitions. Unlike ExtJs that tries to mimic Microsoft type of complexity in it's implementation and richness of widgets, sproutcore follows the apple philosophy. As I mentioned in my previous post, there seems to be some connection betweek sproutcore and Mozilla, which really puts this framework on the map, and somehow gives is a promising future.
It's no secret that a lot of the developers are from/in apple. The two guys that oversee this open source framework work at http://www.eloqua.com a Vienna, VA based company.
I would live to actually start playing with this, but sproutcore is really married to Apple, so unless you are running Mac OSX, you are out of luck.
Also, would like to mention, that sproutcore is being marketed as the HTML5 JavaScript framework, which more of a buzzword... I have not seen seen a radically different HTML5 like approach compared to other frameworks.