The Catalog Python SDK by Brian Samek interacts with the Minuteman Library Network catalog. Via API, developers can obtain a barcode number, sending requests and receiving responses in JSON and XML protocols.
Revel Systems API makes it possible to run a cash register, a restaurant and a mobile point-of-sale system with an iPad as the center of the user interface. Check out what Revel has to say about the API on their website.
Slice, the ultimate online shopping assistant, has launched the Slice API. The Slice API allows third party apps to integrate Slice features such as price drop alerts, tracking packages, spending tracking, email receipts and more. Slice is currently recruiting developers to test the API and build apps upon the Slice platform. Slice is dedicated to changing the way online shoppers interact with the products they buy online, and the Slice API sits at the heart of its mission.