Anything you want to control with Siri. Almost anything is possible but here are some ideas:
SiriControl is a server which enables you to retrieve Siri voice commands directly in your application, granting makers the ability to add Siri voice control to anything imaginable.
With the use of a generated token, it should be fairly secure.
Yes, SiriControl Server can be run locally.
There is also a version that runs locally, written in python without using SocketIO, which can be found here.