‘ggtern’ is a software package for the statistical computing language R. It is an extension to ggplot2  specifically for the plotting of ternary diagrams.
Ternary diagrams are Barycentric plots w/ three variables, and, they are commonly used within the fields of chemistry, petrology, mineralogy, metallurgy, materials-science, genetics and game-theory, amongst others. Whereas a simplex diagram is the general case for , in dimensions, the ternary diagram is the specific case when (producing vertices).
With the exception of the work by Sean Mulcahy  and Darren Wilkinson , there are very few resources on the internet where ggplot2  has been used as a platform for rendering such diagrams, ggtern attempts to bridge this gap, and has since been used within a number of publications as a direct result.
If you are familiar with the syntax of ggplot2, then using ggtern should be a breeze, without too much trouble, it is quite easy to produce publication quality ternary diagrams such as the one immediately below: