Can I zoom out windows or scale the whole desktop?

Disclaimer: I do not know if it works for all graphic drivers. Intel driver here, in 13.04.

First of all get the normal screen you have active:

xrandr --current

My output is:

Screen 0: minimum 320 x 200, current 1024 x 600, maximum 32767 x 32767
LVDS1 connected 1024x600+0+0 (normal left inverted right x axis y axis) 220mm x 129mm
   1024x600       60.0*+   65.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)

Ok, it is LVDS1. Now for example to zoom out at half linear dimension:

xrandr --output LVDS1 --scale 2x2 

The whole screen should zoom out. Now I have:

(0)asus-romano:~/research/reviews% xrandr --current
Screen 0: minimum 320 x 200, current 2048 x 1200, maximum 32767 x 32767
LVDS1 connected 2048x1200+0+0 (normal left inverted right x axis y axis) 220mm x 129mm
   1024x600       60.0*+   65.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)

So the systems thinks it has a 2048x1200 screen. Very useful for crappy programs that thinks you have a gazillion pixel space and do not offer scrollbars in some option windows...

To go back:

xrandr --output LVDS1 --scale 1x1

(You can use 1.5x1.5, too). Look at man xrandr for a lot of fancy things.

Oops. There seem to be a bug in which the extended video zone is not reachable: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/883319 and upstream https://bugs.freedesktop.org/show_bug.cgi?id=39949

A workaround for this is to specify the desired larger area as a --panning option, e.g.:

 xrandr --output LVDS1 --scale 2x2 --panning 2048x1200

It will not cause any actual panning, since the whole large area fits on the screen due to the scaling.