LeDimmer!

Turn Off the Lights for Desktop is a powerful, helpful app to dim your whole desktop and protect your eyes at night. Turn Off the Lights for Desktop allows you to work, play in a dark environment without damaging your eyes. And helps you to reduce eye strains and radiation by breaking the brightness limit of your screen settings. The simplicity in this app let’s you dim the screen with one click on the lamp button. And two finger click, you get a quick settings menu to change the color and the opacity value of the dark layer. »

If you want to concentrate on a task at hand on your Mac, Window Focus is an absolutely essential app. By highlighting the window you are currently working on and have open, all other background windows are dimmed, which minimizes the distraction they cause and helps boost your productivity.

CinemaDrape helps you focus on your current task on screen, by instantly blanking or dimming the other less important areas in a web page or in the background windows. CinemaDrape works anywhere and can help you write an important document, watch an online video, compose an email, or play a browser game. Use CinemaDrape to stop getting distracted by all those side elements, ads, or social network and instant messaging notifications. With CinemaDrape you no longer have to manually clean up your working screen area, close windows, or watch lower resolution videos in full screen mode just to get rid of the disturbing elements. CinemaDrape is very easy to use: adding a new transparent focus area is like drawing a rectangle. You can add as many focus areas as you need. And you can easily move or resize the focus areas using the mouse or arrow keys, save them for future reuse, pause or resume the drape, or change its color and opacity. »

TunnelVision allows you to hide the parts of the screen where your mouse cursor is not, effectively increasing privacy (though at a cost).

Stay Focused is a small app which lives in your menu bar. Its role is to help you to stay concentrate on one task without any distractions. The focus mask will always follow on every workspace.

Clutter Cloak is a tiny anti-distraction program for Windows XP.It is activated by a configurable hotkey, then obscures everything on the screen except the child window immediately under the mouse pointer. (By default the hotkey is Ctrl-F11.)

Windows only: Instantly blank out your desktop and all of your running apps with Dropcloth, a Windows copy of previously mentioned Mac-only app Backdrop.