I got a link from Rachel Sterne, who is NYC's Chief Digital Officer -- asking for ideas for apps for NYC.
They have a site asking for ideas, and they show you what people are submitting.
For example. I just got back from my daily bike ride. I do the same one almost every day. Head west on 9th St, over to Christopher. Cross West St, turn right and head north to 80-something street on the Hudson bike path. Then turn around, come back via 10th St.
Today, while heading south, I spied an electronic street sign around 14th St that flashed by something about the bike trail being closed one day coming up soon. As I rode by one of the piers I could see they were setting up a big concert stage. So I conclude that one of the days this weekend the trail is going to be closed.
The city did a good job of putting the info geographically near where the event was going to be. Now we have to create the intellectual space for the information, so it reaches the people who need it, in time to use it.
It's not a single app, rather it's the architecture for people-oriented information on the scale of a city. Which is smaller than the world, but also richer and more complex. Because in a city like NY people do a wide variety of things. It works. But if the information were more available, it would work better.