See a demo here:
Some ideas of things to do next:
More styles of facets.
Implement positioners, especially for stacked and side-by-side bar charts.
Keys for aesthetics other than x and y.
Size scales for more geometries.
Coordinate systems (esp. pie charts)
Regularize/rationalize/document use of CSS for controlling appearence.
In-browser interactive graphic builder. (REPL?)
This project started life as a Hack Week project at Etsy. I’m no longer there but if you want to hack data or something else at Etsy, they’re probably still hiring. See http://www.etsy.com/careers/