There is no standard way to switch out of fullscreen in Linux right now. Some apps will have a shortcut for it such as F11, Ctrl-f, Alt-Tab or Alt-Enter, but others do not and quitting them might be the only way and if they are buggy not even that might be possible.
For apps running in Wine there is however a workaround. If you run
winecfg go to the
Graphics tab and set
Emulate a virtual desktop you can force all Windows applications to run in window mode. Furthermore you can use
wmctrl to remove the borders of a window. I found that running applications in window mode and having this command bound to a key:
wmctrl -r ":ACTIVE:" -b toggle,fullscreen
Works quite well most of the time, as unlike fullscreen mode done by a game itself, this kind of fullscreen is done by the window manager and you retain normal Alt-Tab control. It however only works with games that run in the same resolution as your desktop.
I have also written some tools to further tweak fullscreen behavior:
But they are not all that user-friendly, but might be interesting if you wanna tweak things a bit further, to disable decorations, keep a window on top and move it to 0,0 would look like this:
windowtool.py -d 0 -a 1 -m 0,0 ACTIVE