Grazr, the startup focused on making integration of structured data from multiple sources easy, has just launched GrazrScript 1.0. What is it? Grazr itself is an application development system for feeds and GrazrScript is a programming language for feeds. It is an interesting product with the potential to make a variety of complex mashup development problems a lot simpler.
You can see a variety of other examples of this in their tutorial page.
As more and more data used to build mashups comes in structured forms like RSS, Atom and OPML, it makes sense to use tools that treat these as first-class data types.