Another one that I like is Collusion. Still listed as experimental though:
Collusion is an experimental add-on for Firefox and allows you to see all the third parties that are tracking your movements across the Web. It will show, in real time, how that data creates a spider-web of interaction between companies and other trackers.
Since they are shutting down the company, are they planning on releasing the code under GPL or some other license for others to make use of it?
What about open source textbooks for elementary school subjects such as math? I'm pretty sure addition and subtraction don't change much.