This is a categorized podcast index available for free (no ads!)
The project is managed by Adam Curry (aka the podfather) and updates his historic iPodder directory.
There's a first podcast episode at the Project Homepage where Adam Curry and Dave Jones (who is an outline guy, developer of the freedom controller aggregator) are talking about the history of podcasting and what's the purpose of this project. They discuss the [big] problems of using the iTunes database and how it influenced the creation of this project. It get's quite technical after the first 30 minutes.
API documentation seems simple enough.
I'd like to see this used on doggcatcher...