The HotelBeds ObjectiveC Sample Code by HotelBeds demonstrates developers how to access the API. It includes API Key access and an example to call the API. With accurate development, users can search databases of hotels worldwide.
The Federal Register is touted as "The Daily Journal Of The United States Government". Its website, federalregister.gov, allows access to the documents published there, which include proposed rules, final rules, public notices, and Presidential actions. It's a pretty interesting and useful look into what the US Government is doing, and how it might affect your life. Amazingly enough, it has a full-featured API, which is a truly open source project, to allow access to the Federal Register within applications.
Practical Management Solutions and Insights (PMSI) has launched an open-source API project for business analytics: dimple. Dimple aims to open up the flexibility and power of d3 to analysts. With little d3 knowledge needed, the dimple API gives analysts access to the tools capable of creating dynamic graphical representations of datasets.