Apps that help you to focus when using a Mac that's chock-a-block full of distractions can be really helpful. iFogg, a US$0.99 app from the Mac App Store, helps you focus by dimming other windows and leaving only the active window at full brightness.
iFogg sits in your menu bar, like many other programs that do similar tasks, and is active the moment you switch windows. The amount by which the rest of the windows and programs are dimmed is adjustable from full brightness to total black-out using a slider on a drop-down menu. You can also adjust whether the app dims all other windows, just windows from other programs, or just those windows not selected, meaning that you can have two windows from two different programs active at the same time.
Dimmed windows can still be accessed, with drag-and-drop, scrolling and clicking unaffected. iFogg can also be quickly turned on and off from the menu bar icon and supports Spaces just fine.
The odd thing about iFogg is that it'll only cover one monitor, so people with multiple monitors won't benefit from the inactive window dimming. You can also select the dimming overlay in Expose, which shows that it's just putting a colored full-screen window overlay on top of all the rest of the windows that aren't active. Still, it works and is pretty light on resources.
iFogg is available now in the Mac App Store. A demo video is embedded below.