My daughter was introduced to Desmos in her 8th grade math class and she's having a blast creating art with it.
The Wikipedia article for Desmos describes it as an advanced graphing calculator and mentions toward the end that “another peculiar use of the calculator involves the creation of graphic arts.”
Sure enough, the Staff Picks: Creative Art link on the Desmos home page reveals pictures of a shark, a chick, a seal, and more.
My daughter made a penguin:
But how do you get started? I clicked “Start Graphing” on the Desmos home page and asked my daughter what to type. She started me off with two equations:
y = 2x + 8
x^2 + y^2 = 8
Suddently, I had created my first graph with Desmos, which looks like this:
I was delighted to see that you can export your graphs (your artwork!!) in SVG format. That means you can further manipulate it in tools like Inkscape.