I have a vague memory of a math worksheet in middle school that required drawing lines with a straightedge, and together lines produced something like a hyperbolic curve:
To me these looked like early 3D computer graphics.
I don't remember what all the worksheet explored, but I do remember exploring on my own in moments of boredom. The simplest evolutions are making the base axes different lengths or angling them relative to each other:
Axes can be joined together:
There's no reason lines from different axes can't overlap:
And there's no reason the axes have to join together at their ends, though disconnecting them does unravel the grid at the fringes:
Of course, there's nothing sophisticated about these, but they do serve as doodle material in long meetings, having enough complexity to occupy one's hands but not enough to distract the brain from listening.