Highcharts, the js charting library used by this Django app, is a very elegant charting library, but users should be aware that it is dual commercial/Creative Commons Attribution-NonCommercial-licensed, with developer licensing for commercial projects starting at $360 for a single dev (although a simple 'non-app' webpage license is also available for $80).
For an extraordinarily powerful js data visualization library that can do charts and much, much more, check out d3.js. If you are good at javascript, spend a few days learning this library and you'll have a tool almost as powerful as Tableau, but that can be run on any modern browser that supports svg (Firefox 2+, Chrome 5+, IE 9+, plus any recent version of Safari, which means it runs on iPhone and iPad).