As a teacher I often use Powerpoint presentations. Sometimes it happens that I have to switch from a Powerpoint-slide to an application to demonstrate something. Here is where the nice little app Isolator comes in handy: Before starting the presentation, I configure Isolator to hide the Dock and show a neutral background color without transparency:
Then I create a button in the presentation and set its action to execute the desired application.
While being in presentation-mode I can start the application with one click. The application runs on a clean screen, with no icons, no background-image and no other applications shown. Exactely the way I want it to be.