gnuplot (no capital 'g') is a tool to plot graphs.
gnuplot example 1:
creating and saving a plot
gnuplot example 2:
creating and displaying a plot
gnuplot example 3:
creating and displaying a wireframe surface plot
gnuplot example 4:
creating and displaying a surface plot
gnuplot example 5:
creating and displaying a contour plot
gnuplot example 6:
creating and displaying a scatter plot- C++ gnuplot interface class: gnuplot interface class