Practical Management Solutions and Insights (PMSI) has launched an open-source API project for business analytics: dimple. Dimple aims to open up the flexibility and power of d3 to analysts. With little d3 knowledge needed, the dimple API gives analysts access to the tools capable of creating dynamic graphical representations of datasets.
Chart APIs are useful and popular, and Google knows how to do them well, so they're continuously adding more features and options for customization to their Visualization API. The Google Code Blog recently highlighted a few of the newest features.
So just how is your App doing? Got calls on your API? How many? StatHat API makes it possible to answer these types of questions statistically and to chart the data to pick out trends and patterns. Seeing is comprehending.