Beaten to the punch by MIT on this one: Scratch. It does most of what I had in my first Design and Education project, which itself was a proposal to extend MIT's Logo Blocks into a more general-purpose multimedia programming application. Admittedly, mine was more of a game than a toolbox, and had a specific narrative structure in mind, but as far as using graphical means for exploring programming goals, Scratch does a really amazing job.

I'd like to spend a few days with this and try to work past the visual bling to get into it as a teaching tool. But I'm encouraged by it and I'd like to see how well it could be used for intro programming classes like CDT Bootcamp.