Windows: You've got a web page, a file folder and a chat window open, and they're all about the same project. WindowTabs, a free-to-try utility, can group together all those app windows with top-most, Google-Chrome-like tabs.
The system tray utility, which used about 11MB of memory to manage five open windows on my system, only does a few things, but it does them fairly smoothly. It adds a tab to the top of your Windows, either on the top-left corner when a window is sized, or as a drop-down, centered tab when maximised. Grab that tab and place it next to another window tab, and the two windows will group, no matter what programs they are. You can drag tabs out of the group again to remove them, and use a familiar Control+Tab keyboard shortcut to switch between open windows in each tab group.
The free trial of WindowTabs doesn't have a time expiration on it, but does limit you to three tabs per group. That's pretty limiting in some ways, but WindowTabs lets you pick and choose which applications it allows tabbing for, either by an inclusive or exclusive list of program executable names. So if you already use Google Chrome, or don't think you want email windows stacked, you can add "chrome" and "outlook" to your exclude list. Alternately, you can use that three-tab limit only for applications where it would really help, like folder views and non-tabbed chat windows.
WindowTabs is a free download for, technically, XP and Vista systems, but it seemed to run fine on Windows 7 as well. Thanks Clem!