Do you want one master switch that turns off devices on 3 circuits?
Or are you looking for something that works kind of like like a non networked 4 way switch where each switch turns off all the lights? (Like switches at two ends of a hallway do?)
ONE MASTER, TWO AUXILIARIES?
As long as all three switches are smart, setting up one master switch is easy, there are multiple ways to do it with or without coding. Even just IFTTT will work.
Or use @NorCalLights ’ trick of not wiring the load in the master, although then if ST goes down you can’t manually turn off the lights on that circuit:
Remote but in wall switch form factor? - #3 by NorCalLights
OR 3 MULTICIRCUIT CONTROLLERS?
If you want to have all 3 switches act as the master, though, then you probably have to install a “button controller” switch like the smartenIt (battery operated) or Enerwave SC7 (wired) at each switch location.
http://www.enerwaveautomation.com/upload/2013041719402075.jpg
Another option is to mount an inexpensive tablet and use a dashboard smartapp like SmartTiles by @625alex or the one by @florianz . Those allow you to control as many things as you like from one location.