gnuplot

Tends to be Ciro Santilli's first attempt for quick and dirty graphing: github.com/cirosantilli/gnuplot-cheat.

domain-specific language. When it get the jobs done, it is in 3 lines and it feels great.

When it doesn't, you Google for an hours, and then you give up in frustration, and fall back to Matplotlib.

Couldn't handle exploration of large datasets though: Survey of open source interactive plotting software with a 10 million point scatter plot benchmark by Ciro Santilli