1. A method, comprising: starting a software application having multiple possible states and multiple possible state transitions, said application having rules specifying computer screen display actions to be performed upon state transitions of said application, said application registering possible states of application said with a state transition registry; placing said application in a current display mode and displaying said current display mode on a computer screen; monitoring the state of said application in said state transition registry , said state transition registry maintaining a list of possible states of said application, including states configured by a user, and corresponding notification priorities, rules, or both notification priorities and rules to be evaluated to determine a new display mode; upon a state transition of said application from a current state to a new state, said state transition not initiated by a user of said application, either (i) said state transition registry requesting said application to evaluate a rule associated with said state transition to determine said new display mode of said application and then said application notifying said state transition registry of said new display mode, or (ii) said state transition registry determining said new display mode from a predetermined display mode associated with said state transition; said state transition registry notifying a state transition handler of said new display mode; said transition handler notifying an operating system to apply said new display mode; said operating system changing a display mode of said application from said current display mode to said new display mode; and displaying said new display mode of said application on said computer screen.