R is a clone of The New S Language by Becker, Chambers, and Wilks of AT&T.
A comprehensive statistics package with a full scripting language, many
statistical operators, load/save, extensive help, graphical capabilities 
including X11, PostScript, HP and other devices. Ideal for interactive
exploration of data.

Once you've installed R, you can start it just by typing R. There is
extensive online documentation; you can start with help() (note that almost 
every S command or function has parentheses after it, so you type
help(A) for info about A).

If you have S users onsite, you may want to "cd ${LOCALBASE}/bin; ln -s R S"