I recently just released a new extension on Qlik Branch. The stream graph is a type of stacked area graph which is displaced around a central axis, resulting in a flowing, organic shape.
You can also convert the stream graph to a stacked area, expanded stacked area, line chart with zoom, stacked bar, and grouped bar. All of this from within the extension using the 'Chart Type' setting.
You can download from Qlik Branch: http://branch.qlik.com/projects/forumdisplay.php?22-Qlik-Sense-Visualization-Extensions
Any questions, just let me know!