I'm trying to figure out how to create a graphical interface, in X11, which exists outside of a window manager's/desktop environment's standard window frame. For example, when Thunderbird finds new mail, it shows a special alert in the lower right hand corner of the screen which is shown without any frame (no close/minimize buttons, etc.).

I'm specifically interested in doing this in QT with C++, but if someone knows a solution with a different graphical library, that would be helpful too.