Lots of features, but slow because written in Python. A faster version may be csvtools. Also some annoyances like obtuse header handing and missing features like grep + cut in one go: csvgrep and select column in csvkit.
Tends to be Ciro's pick if gnuplot can't handle the use case, or if the project is really really serious.
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
Examples:
- matplotlib/hello.py
- matplotlib/educational2d.py
- matplotlib/axis.py
- matplotlib/label.py
- Line style
- Subplots
- matplotlib/two_lines.py
- Data from files
- Specialized
Became very popular as of result of people using Bullet Physics for reinforcement learning AI training robot simulations.
Source code: somewhere inside the main Bullet Physics source tree. Yay.