Collection King, a client of Bsidestudios, wanted to integrate their Drupal website with the app they were developing using PhoneGap. The app makes service calls to the website and the website needs to execute the appripriate function calls and return necessary data to the app using JSON. We used the Services module for that.
We also created custom modules and documentation to provide REST API functionality to Privatemsg, User Relationships and Heartbeat modules. This way the app could use these APIs to perform various tasks, such as creating a new private message, replying to one, viewing all messages and threads for a user, requesting a user relationship, accepting or declining a request, viewing all the relationships for a user and viewing all the activities by a user. We are working on getting these modules into drupal.org.