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Taken without permission from the Humour Group because I thought it would fit better in here.
What he actually does: he's playing train simulator?
It's a mapping program, I think :P
The right lower corner image a mapping tool. UDK, perhaps.
So he's creating a map for a mod.
Yeah, I was going to say it was UDK :P you can tell from the icons on the left hand side. ;)