As an extension on my previous message. I think there are two scenarios for cloning:
- projector use: this typically requires setting both displays to the highest common resolution.
- plugging a laptop to a high-res desktop screen.
In that case one usually will want to use the external display at highest possible resolution.
This is for instance what Nvidia-settings does. It puts both displays in highest res. mode. Ideally, the one with lower resolution should pan.
2) The download instruction for non-Ubuntu on http://willem.engen.nl/projects/disper/
It should link to an archive of disper.