VPaint is "an experimental vector graphics editor based on the Vector Animation Complex (VAC)" (as featured at SIGGRAPH 2015) which can be used for creating vector images and 2D animations.
The developer says that 1.x releases are betas, short on features and with occasional glitches and crashes, and for research and curious artists only.
At the moment that means you're able to draw freehand lines of customisable width (which also respond to pressure on a pen tablet), then "sculpt", "smooth", and generally push them around until they suit your needs.
A simple paint bucket tool fills your object. If you sculpt it afterwards, the filled area updates automatically.
As usual with vector editors, a Select tool allows you to click an object and drag it around.
A simple timeline provides the basis for simple animation. You're able to create separate frames, or copy objects from one frame to another, while onion skinning - overlaying several adjacent frames - ensures accuracy.
When you've finished, your projects may be exported in PNG or SVG format.