...but a way of taming your desktop.
I have to 'fess up. My desktop discipline is appalling. I run two 23" monitors on my main machine (invaluable when laying out books). The trouble with that is that I tend to leave lots of applications visible at a time: NetNewsWire, Mail, iChat and so on all compete for my attention.
So I'm experimenting with Think, a free app for OS X with a simple mission—it hides everything but the application you're using. But, for me, the killer feature is that you can still pop up other application's windows, use them, and then use a simple key chord to hide them again. It seems trivial, but in the two days I've been sing it I've found it fits nicely into my workflow—I want to concentrate on one thing for a length of time, cutting out distractions, but at the same time I need to dip into ancilliary applications every now and then.