Mac: It's easy to get distracted when you have a bunch of different applications open. One bouncing icon and suddenly your focus is gone and you forget what you're doing. You can download programs to keep you focused, but blogger Zack Shapiro points out an old trick in Mac OS X called "single application mode" that keeps your desktop clean.
With single application mode on, the only app that will show is the one you have selected. Everything else disappears but keeps running. Essentially, instead of having lots of windows open all over the place, you get one at a time. It's simple but effective in keeping you focused on the work you're supposed to be doing. To enable it, hop into terminal and type:
defaults write com.apple.dock single-app -bool true killall Dock
To turn it off, swap out "true" for "false" in the first line. Single application mode has been around since Mac OS X was first launched, but it's no longer the default behaviour. Thankfully, it's easy to turn back on.
Single Application Mode: My favourite hidden feature of OS X [Zack Shapiro]