If you could write a video game, what kind of game would it be?

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Or if not a game, what then? What would your dream game, or program, be about, or do for you? I myself have two things I would love seeing: This one is educational; I would like to explore the entire planet, in geographical or topographical sense, in a plane like the one in the old game, Descent, a ship that hovers in mid-air. Some detail would be nice like famous landmarks. And why not some of the planets? Or the moon? If done right, it could be a big hit. Or a submarine simulator, which has already been done, but one that gives you the option of putting all the specific things (your depth, speed, direction, a map, the target's bearing, and so on) all right there in one screen. I have a sub sim, but you have to keep switching screens. Other that these two things, I have no other ideas (no imagination, I guess)....