Go Linux! But open source software is no longer just about the Linux operating system. It may sound like I'm speaking a different language, first let me explain what I mean when I say open source software: Open source software are programs, applications, services and/or operating systems for computers that are completely free of charge. The creators often make the software to satisfy a need whatever the case may be from a web server to a math program for kids. Often these developers start out as college students(that's how Google started) and the continue to develop their product asking for no money from the actual product.
A good example of this model is RedHat (http://www.redhat.com). Redhat develops one of the world's best operating systems - Fedora Linux, and they charge nothing for it, you can download it freely from many universities. So your next question might be: How do these companies make money? I'm glad you asked. They generate revenue in 2 different ways: 1. They also sell an enterprise version of their product for money and 2. They sell support for their product.
This is a complete 180 from the old school model of software practice. In the olden days a company would produce a product and then license their product to people for money(*cough* Adobe).
Moving forward you will see more and more companies moving to the Open source model, many companies are already embracing it and have done quite well. Two example are IBM and Sun microsystems. Both of these companies have endorsed and use LInux and Open source software and give it away for free and offer service contracts to support this software. It's a win win in my opinion.
For more references and resource please see: http://en.wikipedia.org/wiki/Open_source, http://www.redhat.com, http://en.wikipedia.org/wiki/Linux, http://www.linux.org/. Also, if you really would like more info go to Amazon and look under books for Linux :)
Here are some great free applications for elementary school kids:
Tux Paint
TuxMath
And here's a great article with links to lots of applications:
http://www.techlearning.com/showArticle.php?articleID=196604921
Words of Wisdom: The best software is not always the most expensive software.
Here's a fun website to learn the state capitals: http://www.vectorkids.com/maps.htm, it's harder than you think it would be.