Today I continued my devolution from 21st-century science back to preschool arts-and-crafts by making a
pop can pen, which is a cheesy version of a real thing called a "folded ruling pen". That's a very simple and surprisingly modern invention(1995) which allows really dramatically adjustable pen/brush strokes. Imagine a brush you could tune from 1mm wide to 20mm wide in the middle of a stroke.
Still figuring out how to use it. I don't think mine's very good, but it's all I've got until more nibs arrive in the mail.