Wikimapia is a web service that allows users to edit information on a world map in a wiki format. Users of the site can add places, edit them, and get the information previous users have entered. The info there is currently pretty sparse, but the service is rather new. The company also recently released a Wikimapia API that supports getting information from the web service.
Google Maps API is the most popular tool for building location-based services. Now, the Google Maps Operations team is leveraging their experience to collaborate with Udacity and create a free course that teaches students how to integrate maps and location features into websites.
New York City is probably best known for its skyscrapers and millions of people, not the trees that line its avenues. A new iPhone app goes out on a limb to give a little credit to the oaks and maples. And it's doing it thanks to open government data.