You can use xmodmap to remap any
key on the keyboard; in particular, you can remap the right Alt to
act as a Super/Win key.

Create a file named .Xmodmap in your home directory with the
following content:

! free up right-Alt for remapping

remove mod1 = Alt_R



! Right-Alt remapped to Super

clear mod4

keycode 108 = Super_R

add mod4 = Super_R

When you log out and then log in again, GNOME should ask you if you
want to load the .Xmodmap file; answer "yes" and you're ready to
go. (You will only asked once.)

Alternatively, you can load the .Xmodmap configuration from a
terminal at any time:

xmodmap .Xmodmap

There are a few things that can vary depending on the X server version and keyboard model. The following items could help you adapt the .Xmodmap file to your specific environment.

1. Check that your right Alt key is initially on mod1: Issue the command
   xmodmap in a terminal window, and you should get an output like
   this one:

   
   
   

   xmodmap:  up to 3 keys per modifier, (keycodes in parentheses):
   
   
   
   shift       Shift_L (0x32),  Shift_R (0x3e)
   
   lock        Caps_Lock (0x9),  Caps_Lock (0x4e)
   
   control     Control_L (0x25),  Control_R (0x69)
   
   mod1        Alt_L (0x40),  Alt_R (0x6c),  Alt_L (0xcc)
   
   mod2      
   
   mod3        Mode_switch (0xcb)
   
   mod4        Super_L (0x85),  Super_R (0x86),  Super_L (0xce)
   
   mod5      
   
   

   
   
   

   If the Alt_R tag does not appear in the mod1 line but on a
   different one, adjust your .Xmodmap accordingly.




2. Check that your right Alt key is keycode 108: in a terminal window,
   type the command xev, then focus
   the small square window that popped up. If you type the right
   Alt key there, you should see lines appearing in the terminal
   window. Look for a stanza like this one:

   
   
   

   KeyPress event, serial 25, synthetic NO, window 0x5000001,
   
       root 0xbd, subw 0x5000002, time 867397196, (53,48), root:(54,49),
   
       state 0x0, keycode 108 (keysym 0xffea, Alt_R), same_screen YES,
   
       XLookupString gives 0 bytes: 
   
       XmbLookupString gives 0 bytes: 
   
       XFilterEvent returns: False
   
   

   
   
   

   The number after the keycode word is the one you want in your
   .Xmodmap file for remapping right Alt.