I’ve had an issue with Counter-Strike Global-Offensive + Mumble when playing, I use Left-ALT as push-to-talk button and when I wanted to show the scores it switch to the desktop.

I’ve installed AutoHotKey, free and open-source software and edited the config file like so :

#IfWinActive Counter-Strike: Global Offensive
LAlt & Tab::Send {Tab Down}
LAlt & Tab Up::Send {Tab Up}

Reload the script and tadaaam, no more Alt+Tab problems in-game, still works fine in Windows.