100 Opensource possibilities, made by the people, for the people!

http://ajaxflakes.com/open-source/a-list-of-the-best-free-opensource-software-for-windows-xp-and-vista/

All of the opensource programs give the people to create their own resources, and can be broken down, with examples from many languages. I can't imagine learning to program for its own sake, and a source file of a program that is interesting can make learning more practical. One example was celestia an astronomical program with source forge. There was a basic program, but to include many of the interstellar features, there needed to be changes on data files to include new textures,objects and locations.
This is as opposed to proprietry software with locked source codes.
Open source freedom means far more than no price.
While you can use programs you can also help improve them.