I do quite a lot of doodling in Windows Paintbrush — usually pixel-by-pixel editing under very high magnification, combined with copy-and-drag replication of patterns. No particular reason; it’s almost automatic, and something I might do while listening to a podcast or waiting for a video to load for example.
Here is one of my favourite doodles from 2009. The appeal for me lies in its deceptive simplicity. If you group the parts into spirals, the whole design turns out to be quite simple. However, the brain insists upon grouping the parts into patches of parallel lines, which makes it look much more complicated than it is.
[Everything below is an update not originally part of this post.]
Here is a fractal doodle that I drew in Paintbrush in July or August, and have decided to merge with this post. I didn’t set out to draw a fractal, but one emerged spontaneously from the iterative algorithm that I used. Basically, I drew a black pixel surrounded by six other black pixels in an approximation of a circle fully surrounded by six more circles, and then repeated this pattern using the composite shape at each level as the new circle approximant in the next.