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.
The site explains the service in general:
Welcome to Lemonade Stand, a new and easy way to buy and sell locally. Lemonade Stand is a neighborly commerce platform that enables people to buy and sell goods within a community. Artists, craftspeople and entrepreneurs can share their wares with their neighbors while members of the community can find and buy close to home. An easy way to shop while supporting your local economy and the talent within it- what could be more wholesome?
The Lemonade Stand API is, as usual, a RESTful service. Replies are in simple XML or JSON. Unlike many other APIs, this one does not require any sort of developer key. It allows developers to look up all listings, a specific listing, create new listings, or modify existing listings. To modify an existing listing, a program needs to store a sort of key made when creating the listing, called a management_url.
Listings include a description, contact phone number, image, and location as latitude and longitude, as well as a unique item ID. With this API, a developer could make a fully functional Lemonade Stand client, as well as integrate any of that functionality within another mashup. One of the things that amazes me the most is the lack of a developer key or any sort of user management. This makes things a lot easier on developers, but perhaps harder on users of the service.
The service and API are quite new, but I expect to see it used in pretty amazing ways in the future.