this project show you how to control the 2 most famous mac music players (iTunes & Vox) with an arduino through the serial port and an app which is free to download
http://www.instructables.com/id/Control-your-mac-music-player-with-arduino/
Control your Keynote presentation with arduino
this project show you how to control your keynote app presentation on a Mac with arduino through the serial port and an app which is free to download
http://www.instructables.com/id/Control-your-keynote-with-arduino/