Just out of curiosity, HN seems like a good place to ask: Does anyone actually here use unix-likes in a multiseat fashion, like they were used 30-40 years ago? Like described here:
https://en.wikipedia.org/wiki/Multiseat_configuration
http://www.x.org/wiki/Development/Documentation/Multiseat/
And if you're on arch linux this is a good start:
If I remember correctly, I had to bump the computer up to 6GB of RAM. She was running off the motherboard's built-in video card and I had two monitors on a separate card.
Eventually Ubuntu changed things so that it wouldn't work anymore, but I believe that it's possible to do now. If you have kids this would be a cheap way to give them all a decent amount of computing power.