I’ve played around a little bit with Scratch, which I wrote about a little while ago. Now I’ve come across Squeak, an open-source version of Smalltalk (for an unintentional pun) with multimedia facilities, aimed at both creating applications for kids and as a tool for kids to write their own programs. According to the website, Squeak grew out of a project at (and is still licensed by) Apple, which is something I hadn’t expected.
There’s a very frame-intensive but otherwise interesting site called Squeakland that’s aimed at educators and has a bunch of applications created by kids (on an internal page that’s not easily linked to). Evidently there’s going to be a SqueakFest conference in Chicago in August. And other projects have grown out of it, like Tweak, which describes itself as "a media authoring environment for children of all ages."
Squeak has at least one advantage over Scratch: It’s available for Mac and Unix environments as well as Windows. EDIT: Oops. Scratch is in fact available for other platforms, and was evidently developed using Squeak! I’m going to give Squeak a try over the next week or so, and if there’s interest I’ll post again with my thoughts.