title: Bar chart in Javascript: stacked bars + grouped bars
body: <p>I'm looking for a Javascript solution to mix Grouped and Stacked Bars with a beautiful graph, such as those provided by <a href="http://vis.stanford.edu/protovis/" rel="noreferrer">Protovis</a>.</p>
  
  <p>For example if I want to compare downloads on Apple (iPads+iPhones) devices to Android devices, I might have (excuse my terrible ascii art)</p>
  
  <pre>
  
  60k |             ^
  50k |    #    ^   ^
  40k |#   #    ^  #^
  30k |@   #^   ^  #^
  20k |@^  #^  #^  @^
  10k |@^  @^  @^  @^
     =================
      Jan Feb Mar Apr
  
  Legend
  #: iPad Downloads
  @: iPhone Downloads
  ^: Android Downloads
  </pre>