Siri is what its founders call a "do engine" as opposed to a search engine. It's a very nifty phone app that lets you speak commands like "get me a table for 2 at a french restaurant that serves scollops tomorrow at eight." and Siri will do just that in a matter of seconds.
Skip till 22.40 for a demo.
This is a great way of using exiting APIs out in the wild and mash them up to do something truly usable for its users.