ggtern
An extension to ggplot2, for the creation of ternary diagrams.
ggtern is a package that extends the functionality of ggpot2, giving the capability to plot ternary diagrams for (subset of) the ggplot2 proto geometries. Ternary diagrams are used frequently in a number of disciplines to graph compositional features for mixtures of three different elements or compounds. It is possible to represent a coordinate system having three (3) degrees of freedom, in 2D space, since the third dimention is linear and depends only on the other two.
The ggtern package is based on (extends) the very popular ggplot2 package, which is an implementation of Wilkinsons "The Grammar of Graphics", and, makes provision for a highly methodical construction process for the development of meaningful (graphical) data representations. Of course, the above book by Wilkinson outlines the theory, whilst Hadley Wickhams ggplot2 implementation is where much of the magic happens, and, an ideal base-platform for the ggtern package.
For further examples and documentation, please proceed to the ggtern website.