[Tikz][1] (a self-referential acronym for *Tikz Ist Kein Zeichnenprogram*)<br>
It's an excellent, and extremely versatile drawing program.<br>
I highly recommend it.


Here's an extensive manual: https://pgf-tikz.github.io/pgf/pgfmanual.pdf

This manual might be frightening at first sight, but it in fact starts very gently, with a long list of worked examples (starting on page 30).

There's also some humorous examples of things not to do when designing a graphic (check out the stuff around page 99). 


  [1]: https://en.wikipedia.org/wiki/PGF/TikZ