Similar to us developers who keep scouring sales rank information on sites like Applyzer there is a service for book authors. It goes by the name NovelRank and it lets authors track their book sales on Amazon.com.
Dave Wooldrige from Electric Butterfly (also a renowned book author in the iOS sphere) took it upon himself to create a beautiful iPhone client for the NovelRank service and released this just today, for FREE.
I’m specifically mentioning this here on my blog because Dave implemented my DTChartView component to get interactive scrollable charts for the ranking data.

