FGDesktopLoupe is a desktop dimmer that will allow you to use a spotlight beam that follows your mouse pointer to focus on a part of the screen.
FGDesktopLoupe allows the user to quickly set the size of the spotlight and the color of the dimmer background. You can use CTRL ALT to open the settings window and CMD ALT to toggle the dimmer effect on or off.
NOTE: FGDesktopLoupe can only be downloaded via the Mac App Store (the download link redirects you to its App Store page). To purchase/download applications via the App Store an Apple account is required.