R is an open source implementation of the S language ("GNU S").
Note that R is now a widely used standard software, backed by a strong and highly active user/developper community) that is now not only used as such but is more and more integrated with other software prokects. For instance both PASW Statistics (formerly SPSS Statistics) and Statistica let you use R as it were part of the software; GGobi can be used in tandem and many other open source programs use R to provide ressources they lack and/or add closely integrated features that R is lacking.
S is the original software developed by Bell Labs (S and New S), S Plus (S+) is the commercial version.
As both S and R are base on the S languange, most S-macros run without modification in R, unless they use highly specific graphics functions or other specialized libraries.
eugen.horber (at) politic.unige.ch