Today I faced really tight situation on my Mac with Skype (yes, again!) - it went unresponsive, and was not reacting on standard shortcuts, and I wasn't managed to close the app by standard means.
I tried to use the keyboard combo: ⌘ Command + ⌥ Option + Esc simultaneously, but it haven't open the "Force Quit" dialog this time.
I tried to call Activity monitor - but it was not possible either, as the App prevented me switching to something else or to open other applications... no standard means worked, even "Spotlight search" was unresponsive by keyboard shortcut. But I knew it still reacted on the keyboard, as caps-lock was working, plus I managed to power off external display, and the to power it on again via keyboard shortcut.
I'm wondering if is there any fallback for these situations, when an Application is totally unresponsive and prevents me from running other apps? It's the first time the app hanged the whole Mac that heavily, that I was unable to kill it or to open any other application to manage the processes.
Is it normal behavior at all, I was counting on it not possible to hang the whole system on a Mac, and one App can't make it totally unresponsive (OS X El Captain, 10.11.4)?
Update: found such the keyboard shortcut I never used: ⌘ Command + ⌥ Option + ⇧ Shift + Esc held for 3 seconds - forces quit of front-most application... not sure if it would work.