I just discovered this cool little application today and love it so far. Credit of the discovery should go to Merlin Mann who showed it on the MacBreak video podcast.
Here is my one-line description: Spirited Away hides inactive applications after a predetermined time.
Often, when I am working on an application, or even web-surfing, I easily get distracted by other programs that fill up the screen. Spirited Away solves my dilemma by hidding other inactive applications. I have set the threathold to 10 seconds, but many people found it too agressive and opt for somewhere between one to 10 minute instead.
Spirited Away also allows the user to specify an exception: just click on the Spirited Away icon at the top menu and click on the application that you wish to exempt. For example, the user might want to exempt instant message (IM) applications such as iChat or Yahoo Messenger.
Since I like the application, I wanted to learn more about it. However, it seems Spirited Away has not seen an update since 2003, too bad. Nonetheless,Spirited Away works well enough that I will keep running it for a long time to come.