I've created several APIs for various Faith Life Church things. The main API page lists the available ones (along with descriptions, links, and examples).
Life started with the lowly XML file (actually, it started with proprietary, flat-text, databases). I started making podcasts for the MP3 downloads. That led to using XML for content. That led to dynamically re-creating the XML content with PHP (some people keep forgetting that
Wow, that's a lot of text and links. It's worth it, though. This has really become a cool thing, to me. As I start to work on more projects, I realize how useful available data is. Since things like XML and JSON are such widely-used formats, everything supports them.