Last time I checked LabPlot, QtiPlot and its fork SciDAVIS had no option for ternary diagrams.

You can try out Veusz: http://home.gna.org/veusz/examples/#ternary, but it does not look trivial.

I am not aware of any other open source, multi-platform program for ternary diagrams (though it is possible to do it with gnuplot with coordinates transformations and some lines for the axes).

As free but closed source, you could give a try to ProSim Ternary Diagram. It probably works with Wine for Linux users. Not many options, but does the job.

http://en.wikipedia.org/wiki/Category:Free_plotting_software

Thanks for sharing that, but have you used any of these packages to do what I am asking about?

I like package LabPlot. http://labplot.sourceforge.net/

Thanks for your valuable input.

Last time I checked LabPlot, QtiPlot and its fork SciDAVIS had no option for ternary diagrams.

You can try out Veusz: http://home.gna.org/veusz/examples/#ternary, but it does not look trivial.

I am not aware of any other open source, multi-platform program for ternary diagrams (though it is possible to do it with gnuplot with coordinates transformations and some lines for the axes).

As free but closed source, you could give a try to ProSim Ternary Diagram. It probably works with Wine for Linux users. Not many options, but does the job.

http://www.chemix-chemistry-software.com/school/ternary-plot.html

http://www.lboro.ac.uk/microsites/research/phys-geog/tri-plot/index.html

Ternary plots can be made using gnuplot. A simple script for that is available here: https://staff.aist.go.jp/a.noda/programs/ternary/ternary-en.html