With Lemonade Stand, users can search for things to buy in a location-based manner, or add their own listings of things they wish to sell. The application is currently available as a client for Android, with a possible Windows Phone 7 version on the way soon as well, from a 3rd party developer that released an early version. Its Lemonade Stand API allows other developers to either code their own clients or use it in mashups.
One of the most important--and too often forgotten--pieces of a successful API is promoting what developers have built. Doing so should be a win-win, as both platform and developer should benefit from third-party apps being discovered by users. Location-sharing service FourSquare just re-vamped its application gallery and now any developer can be included.
Take a look at our API directory and you will quickly note that the Google Maps API continues to reign as the most popular API used for mashups. As the API continues to gain momentum, several new utilities have emerged to improve the user experience (or UX as it has come to be known).