title: Library/tool for drawing ternary/triangle plots
body: <p>I need to draw <a href="http://en.wikipedia.org/wiki/Ternary_plot" rel="noreferrer">ternary/triangle plots</a> representing mole fractions (<em>x</em>, <em>y</em>, <em>z</em>) of various substances/mixtures (<em>x</em> + <em>y</em> + <em>z</em> = 1). Each plot represents iso-valued substances, e.g. substances which have the same melting point. The plots need to be drawn on the same triangle with different colors/symbols and it would be nice if I could also connect the dots.</p>
  
  <p>I have looked at matplotlib, R and gnuplot, but they don't seem to be able to draw this kind of plot. The 3rd party <a href="http://cran.r-project.org/web/packages/ade4/" rel="noreferrer">ade4</a> package for R seems to be able to draw it, but I'm not sure if I can draw multiple plots on the same triangle.</p>
  
  <p>I need something that runs under Linux or Windows. I'm open to any suggestions, including libraries for other languages, e.g. Perl, PHP, Ruby, C# and Java.</p>