Swap Left Alt with Left Win in Saucy (13.10)

The layout options can be changed in gnome-tweak-tool, in the "Typing" section. The setting to configure "Alt/Win key behavior" is the last one in the list.

You can use the following commands in terminal to swap Left Alt with Left Super:

xmodmap -e "keycode 64 = Super_L NoSymbol Super_L"    #this will make Alt_L to act as Super_L
xmodmap -e "keycode 133 = Alt_L Meta_L Alt_L Meta_L"  #this will make Super_L to act as Alt_L

To get this change for every session, after you have run the ​​previous commands create a file called .xmodmap with the new keymaps, using the following command:

xmodmap -pke > .xmodmap

Then, create a file called .xinitrc in your home directory, containing the following line/command:

xmodmap .xmodmap