In windows we have the sistray concept.
When an application is minimized to the sistem tray, it keeps running but its windows won't be accessed in the alt tab cycle.
In fact, it is running on background. When you need to bring the application to the front, you go to the system tray and activate its icon and then it's ready.
For apps like mail or skype this is wounderful because you need those running but you don't need their main window bothering you when you're cycling to first plan apps.
Is there a way of getting this wo work in a similar fashion on Mac OS?