This is Kerbal Space Program. It's a game about space.

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And this is Achron. It's a game about time.

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It's the only videogame with a fully realized "real time" time travel mechanic. If I recall correctly, they even designed the Resequence engine (the thing that makes Achron possible) so that other games could be built off of it. If only somebody could/would combine the two. Time-travelling orbital mechanics sound amazing.