This image was taken in LibreOffice due to the unavailability of gnuplot at the time of needing it.
Gnuplot (technically gnuplot) is a command-driven interactive function plotting program. Put in simpler terms: it is a very powerful graph plotting tool that you can use by giving it a set of instructions or commands, rather than using a GUI or window.
This tutorial goes into how to create a line graph from a csv using gnuplot. Why gnuplot? Find out after the jump.