When "concentrate" mode is activated, all windows except for the current active window are smoothly faded out. The purpose is to dim everything on all of your monitors when you need to get to work. In this mode dark area should be "click through" to easily pick a working window.
Jedi:
https://web.archive.org/web/20070106070119/http://www.anappaday.com/downloads/2006/09/day-10-jedi-concentrate.html
LeDimmer:
https://sites.google.com/site/llemarie/ledimmer