Following on from Christian's comment, I had a look at the [Superfund ring-chart][1]. Below you can see it in action. Each segment goes live when the mouse hovers over or near it. By clicking and dragging the mouse up or down, the value of that sector increases or decreases respectively. There's also a popup that appears next to the sector, where you can click to delete the sector entirely. And to the left of the ring-chart (and not shown in the images below) is a list of extra categories that you can add to the ring chart. The linked ring-chart is done in Flash. I guess it could be done with Canvas and Javascript too. There may already be a library out there for it.

![enter image description here][2]

![enter image description here][3]


  [1]: http://www.superfund.com/tools/PortfolioTable/index-de-AT.html
  [2]: https://i.sstatic.net/z5QD6.png
  [3]: https://i.sstatic.net/5S6Ur.png