This is a (very old) AutoHotkey script which I made back in my competitive TF2 days to enable running at extremely wide resolutions on not-extremely-wide monitors, provided again by request.
The problem with that usually is that the desktop shows behind and can be quite distracting. This script does three things:
- Hide the desktop and taskbar
- Black out the area behind the focused window
- Set the focused game to always be on top
Once in the selected game (see windowTitle, TF2 by default), you can enable the effect with Ctrl + F12.