App Inventor. It uses the Open Blocks Java library to allow visual creation of applications, online.
This could be useful for regular developers to prototype quick apps. But, the real use is for non-developers or young folks. What would your kid create if they could create something with no coding required? Might it be silly? Might it be something other kids would have fun with? If you're not a developer, what would you create?
The tool, as it stands now, isn't fully open to the public. You have to fill out a form and then Google will eventually add access. The form is definitely aimed at educators. It's clear Google is looking at this as a teaching tool of sorts. We've always thought mobile programming would make a great target for teaching. This is evidence we aren't alone in that thought.