The Groupon Java Library by Jessica Chung interacts with the API, that allows to build Groupon applications. Developers can improve, add extensions, and create multiple platform interfaces considering groups of clients who want to find the best deals nearby. Groupon official site offers an API developer forum.
It's often said that in New York City everything comes down to real estate. The tenth API to emerge from the New York Times developer network addresses this topic with pricing data for the five borough's residential properties.
In Chicago today eBay will kick-off of their annual eBay Developer's Conference by announcing Project Echo, a way for outside developers to integrate their apps "directly onto the world's largest ecommerce site".