Lively Kernel is another one of these technologies from Sun that is tantalizingly cool, but hopelessly unfinished enough that you really can’t commit to develop against it in a non-trivial way. Having it only work properly in Safari pretty much dooms it to obscurity. It is supposed to work in Firefox, but for me it only displays about the top two inches of the demo and that is it.
I think one of coolest features of all is that it is SVG-based under the covers. I think that SVG is a real sleeper technology that is going to emerge as an extremely powerful way of getting scalable user interfaces that go from mobile to desktop (and beyond).
Intro from Sun’s site: