Stack Overflow, the very successful question and answer site for programmers, have now released their own API into public beta. The API actually works with all of the Stack Exchange sites, including serverfault.com and superuser.com, with more sites possibly launching in the future. The API is supported by the site http://stackapps.com.
The importance of providing an API for your application, irrespective of its intended use case, cannot be overstated. In this tutorial, Itay Herskovits explains the basics of RESTful architecture and how the Backand platform can be used to automatically build a REST API for an Agular application.