A common problem in today's world is distraction - too many applications open, too many emails showing up, etc, etc. Large screens give a tremendous boost to productivity but this often turns into having more applications open distracting you. And let's not mention email, RSS feeds and IMs constantly chiming away.
Thanks to the wonderful design of Mac OSX there are several utilities available to help lessen the distractions by hiding all applications other than the one you are working on at the time. Some of them, like Think and Backdrop have one fatal flaw - they require you to use their custom application switcher to jump between your apps, rather than integrating with the operating system's built in one. Thankfully someone worked out a way to do it right and Isolator was born.
Isolator is a very simple application. It doesn't launch as another app in your dock, instead it sits in your (albeit overcrowded) menu bar, and provides only a few sparse settings - the background color to use, whether to make the backdrop opaque (so you can see the desktop underneath it), whether it should start when you log in or activate automatically, and what key shortcut should activate/deactivate it. Once activated, all but your current application are hidden and your chosen background color fills up behind the window(s).
Having only used it for a short while I can't proclaim how it has saved me x hours per week or saved the lives of thirty-three cats, but even after my limited use it looks to be an app well worth using. And, given its cost there's no excuse for not trying it (presuming you use a Mac).