My partner put together some really nice intro animations to help users understand some of the finer points of drawing between the lines.

I wrote a slightly too complicated smoothing algorithm to fix any drawn curves that may have some extraneous handles.
I've worked really hard to make the pencil tool match how an experienced designer would add bezier handles, but sometimes it needs a bit more of a nudge.

Originally it was just a layout engine for SVGs that you had to put together in some other vector program. However, that process was annoying and out of reach for most hobby crafters, so I built out a very nice font editor with a lot of attention to stylus support on tablets.