Windows: If you have a lot of "always on top" apps running on your PC, maximised windows can throw a wrench into your workflow. Free app MaxMax changes Windows' default maximise size so your maximised windows don't get in the way.
MaxMax sits in your system tray, from which you can configure your windows' margins. Just define, in pixels, how much room you want to leave between maximised windows and any side of your screen. You can configure different sets of margins for multiple displays, too, as well as suppress its behaviour by holding Shift (or another definable key) while maximising a window. It's nice to have if you, say, use Windows 7's widgets, or like to have your buddy list visible at all times (or if you'd just rather see your pretty desktop instead of a bunch of white space on web pages).
MaxMax is a free download, Windows only.