Most of the software mentioned in the resources comes under the category of “Open Source.”

The basic idea behind open source is very simple: When programmers can read, redistribute, and modify the source code for a piece of software, the software evolves. People improve it, people adapt it, people fix bugs. And this can happen at a speed that, if one is used to the slow pace of conventional software development, seems astonishing. (from opensource.org).

For more information on the Open Source Initiative (OSI), a non-profit corporation dedicated to managing and promoting the Open Source Definition for the good of the community, specifically through the OSI Certified Open Source Software certification mark and program, check out the OpenSource.org website. For the Open Source Definition, check out this page.