Gnuplot

Gnuplot is an free program to create plots which can be used for easy data exploration, or to add to presentations. Plotting is defined by a declarative language, which means you can reuse your script with little to no effort. It can be used to automate chart production for reports or web pages.

Gnuplot can produce a wide variety of 2D and 3D plots, with lots of customization, allowing to produce interactive charts, and/or good looking static charts, take a look at the gallery. The results can be saved in several formats, including raster files, like gif, jpg, tif, and vector graphics like svg, emf, dxf.