This is really cool, apparently you can use it to aggregate RSS feeds, or make a super-awesome multi-search program. Or just about anything else you can come up with. It uses the massive bandwidth available of Yahoo, and the magic of Ajax to let you make your own mashup, just by dragging and dropping little objects.
Think The Incredible Machine except with websites and stuff.
To see what this thing is truly capable of, check out this: 10 Pre-made searchable pipes.