Features include: fading the line as you draw it (f), showing tangents of your movement (t), animating the tangents as they appear (a), changing the color of the line, saving the linework as an SVG file.
Let me Paint you a picture
One of my sources of inspiration, when I started my career, was Evan Roth, a digital artist based in Paris. He worked on a project called Graffiti Research Lab, which struck a cord with me. I had always had an interest in combining technology with graffiti and seeing this showed me there were other people interested in doing the same, and there were lots of possibilities.
My first website skribbs.com[v2] was made in Flash and one of the features of the site was the 'Relax/Play' page which let the users tag the sky. The original idea had a lot of controls. The ability to change the thickness of the strokes, the number of paint drips, and the paint color.
Now that HTML has finally come up to the level of interaction the Flash did back in the day, one of my first (and ongoing) projects is to recreate and enhance the sky-tagger. I know there are lots of tools that exist out there, but it never hurts to understand the underlying concepts.