The open-source programming environment R is one of the most powerful exploratory data analysis packages available today.  Because it is open-source, it is freely available and has become an extremely popular medium of exchange for new data analysis methods and ideas.  The Comprehensive R Archive Network (CRAN) maintains a website that provides access to the basic R environment, a large number of add-on packages, download instructions for installing the software in a variety of different environments (including Linux, Windows, and Mac OS), detailed documentation on how to use the software, and much more.  Additional information may be found at the following URLs:

• General information on R: http://www.r-project.org
• Detailed download instructions: http://cran.r-project.org
• Available add-on packages:
  http://cran.r-project.org/web/packages
• Documentation: http://cran.r-project.org/manuals.html