Squeak is an open source educational programming environment. "Squeak's main purpose was to provide a playful and empowering arena for kids to learn important ideas." For those of you that remember Logo, it has some of that feeling to it, but it is oriented around multimedia. This software could be extremely useful for math and science projects. It also looks to be an excellent means to teach a programming language.
Examples of what Squeak can do (PDF). Here is the Squeakland web site.