"R
[http://www.r-project.org]
is a language and environment for statistical computing and
graphics" [http://www.r-project.org/about.html].  For more background on R ...

R apparently binds to [Tcl], [Tk], and [Visual Tcl]
in ways that have not yet been clearly described
[http://www.r-project.org/nocvs/mail/r-announce/1999/0023.html].