Force Quit is an extension that adds a 'Force Quit' button to the top panel of gnome shell, the UI of Gnome 3. Clicking the 'x' icon from the left of the gnome-shell panel changes the cursor into a 'x'. Then, click over a non-responding application to kill it instantly.

Handy if you're prone to working with unstable software grin

[Note: This extension isn't maintained any more.]

This extension employs 'xkill' on the backend.

Installation

From Gnome Shell Extensions Directory:
https://extensions.gnome.org/extension/102/force-quit/

Or Manually

Download:

cd ~/.local/share/gnome-shell/extensions
git clone https://github.com/isDipesh/gnome-shell-extension-force-quit.git
mv gnome-shell-extension-force-quit/ force-quit@isdipesh

Restart Gnome:
Alt+F2 to open run command prompt
Enter r

Enable Force Quit Extension from Extensions from gnome-tweak-tool.

Superpiffer has created a package for archlinux in https://aur.archlinux.org/packages.php?ID=55879.

If it doesn't work on your system, maybe you don't have xkill installed.
jjmarin on GSE says "In fedora you need to install the package xorg-x11-apps in order to get the xkill".