Yahoo Pipes let’s you build your own mashups by dragging modules. The Yahoo Pipes project makes it easy for you to easily direct data through a series of loosely connected applications. Tony Patton offers a really great tutorial.
This video introduces the mashup concept.
There are a few cool Pipes currently running: (note, you may need to log in to yahoo to view source), NYTimes thru YouTube, NYTimes thru Flickr, Apartment near something (make sure you hit ‘run pipe’ to see results), and those just scratch the surface.