How much will it cost to hire that cabbie? The Yourtaximeter API gives access to such precise data that cab companies in the UK rely on it to give quotes. Yourtaximeter provides a tool anyone can use to calculate a fare. The API documentation, other than providing a link to where you can get an access key and noting responses are flexibly delivered in JSON or XML, is rather skimpy. That's actually a complement: minimal documentation reflects the fact that no coding skills are required.
Yourtaximeter has an interesting second feature: revealing whether the car you are about to hire is really a cab. You might be tempted to say, of course I can tell--there's that sign on top and a meter inside. Well, yes, but when is a cab not a cab? When the license plate isn't registered as one. Yourtaximeter has a free iPhone app that not only calculates cost, but can also validate the plates as a registered cab. (Sorry Android users; you'll have to take your chances, at least for now, until their Android app becomes available.)
Sometimes, less is more. One of the APIs returns only the name of the district you are in, just for a location. If you're calling for a cab at the corner of Smith and Albert... which Smith and Albert is it? That app will tell you--so you can tell the company where to pick you up.
Apps like these could destroy brain matter in London cabbies. They have to pass a detailed test of the city that is so rigorous that the process of studying for it actually promotes growth of brain cells in certain areas, similar to what happens to musicians who practice intensively; their brains branch out differently. But if these apps make all that mental mapping no longer necessary... who knows?