Jedi Concentrate is a very useful application that fades out every part of the screen that does not belong to the active window. You can download it from the great website an app a day. The application is open source and uses only 44 Kb unpacked. All you need to do is unpack the application to any place on your hard drive and run it from there.

Once Jedi Concentrate has been started you see its icon in the system tray. To activate the feature you simply press F12 and everything fades to a dark color except the active window which stays the same.
Ghoster is a similar freeware application that dims all windows except the active one.

How to minimize every window to the tray
Alt Tab Thingy Window Manager And Alt Tab Replacement
Hide Windows with Watchcat
Automatically Prioritize The Active Application
There Are No Active Mixer Devices Available
Try Zorro 1.5
Description
Zorro is a utility to completely blank the screen except for a rectangular area selected by the user. This is especially useful for watching videos on your computer without being distracted by other programs.
http://www.gabrieleponti.com/software/#zorro