Mac OS X only — that I know of, any word to the contrary is welcome.

I was doing some Wordpress development this weekend while listening to my team on MLB Gameday Audio. While I attempted to Cmd-Tab to another application I miskeyed and hit Cmd-` (` is right above Tab on my keyboard) which gave me a pleasent surprise.

Because MLB Gameday and Gameday Audio each open in their own windows I typically resorted to using F9 to move to either of those windows. However, as long as I’ve got Firefox (or any application for that matter) I can use Cmd-` to cycle through the open Firefox windows. This goes for Finder windows, open photos in Photoshop, open documents in Word, etc. Great time saver.