From <http://www.R-project.org/about.html>:

    R is a language and environment for statistical computing and graphics.
    It is a GNU project which is similar to the S language and environment
    which was developed at Bell Laboratories (formerly AT&T, now Lucent
    Technologies) by John Chambers and colleagues. R can be considered as a
    different implementation of S. There are some important differences,
    but much code written for S runs unaltered under R. 

    R provides a wide variety of statistical (linear and nonlinear modelling,
    classical statistical tests, time-series analysis, classification,
    clustering, ...) and graphical techniques, and is highly extensible.
    The S language is often the vehicle of choice for research in statistical
    methodology, and R provides an Open Source route to participation in that
    activity. 

    One of R's strengths is the ease with which well-designed
    publication-quality plots can be produced, including mathematical symbols
    and formulae where needed. Great care has been taken over the defaults for
    the minor design choices in graphics, but the user retains full control. 

WWW: http://www.R-project.org/