ctioga2 is a plotting program in the spirit of gnuplot. It can be used either directly on command-line or writing command files (or a mix of both). It produces publication-quality PDF files. It is based on the Tioga plotting library.
FRIDA (flexible rapid interactive data analysis) is a generic program for manipulating, fitting, and plotting x,z,y data. It is primarily aimed at spectral analysis, especially in neutron scattering. Note: project has moved away from sf.net.