alt + tab application window switcher (e.g. no grouping of windows) in ubuntu

sudo apt-get install compizconfig-settings-manager
sudo apt-get install compiz-plugins

Open compizconfig-settings-manager with alt-F2, type ccsm.

Scroll down to “Ubuntu Unity Plugin”. Choose the tab “Switcher”. Disable the alt-tab and shift-alt-tab key bindings. (“Key to start the switcher” and “Key to switch to the previous window in the Switcher”.
Click the “Back” button.

Scroll down to the “Window management” section. Here you can select another switcher.
I enable the “Static Application Switcher”, resolve any potential conflicts by setting the setting for “Static Application Switcher”.
Now you can tweak the switcher by clicking on it. I have changed alt-tab and shift-alt-tab to “Next window (All windows)” and “Prev window (All windows)”.