Think is an application which allows you to stay focused on one task. When you launch it, the illumination panel will allow you to select the window you want to focus on. The Desktop and other applications are kept behind it to keep you focused on the illuminated app. You can temporarily bring a "guest" application above the backdrop by clicking on another app in the Dock. Clicking into the backdrop will refocus you on the illuminated application, returning the guest to exile. Think's Dock icon serves two purposes. First and foremost, it's a convenient way to raise Think and show the illumination panel. Clicking on Think in the Dock is the same as clicking the raise button in Think's control panel. Secondly, Think's icon displays some useful information to you. Notice that when there's an application illuminated, its icon is displayed inside Think's icon. Because clicking in the backdrop refocuses the illuminated application, it helps to know which app is currently illuminated. You can glance at the Dock if you ever need to know - Think will keep its Dock icon updated to help you remember! Not that you'd ever forget, of course.