Mine is a game in which you can create planets that will look any way you want, create life for the planets, and put plants and different fruit on them too. Or, you can just create some humans, and I mean Sims 3 editing quality, you can also give them personalities, and the game would have some way to know what the kid would look like from combining the parents.
You can travel through time, watching them build up straw houses and such, then drop a rock on one, burn another, burn humans, throw humans, drown humans, put different tribes into wars, and just tinker with their lives in any creative way you can think of.
For instance, you can possess someone, maybe multiple people, and have them go on killing sprees. As society collapses one, from not have any women to have children, and two, because almost no one is left but a handful of men. If you drive one mad enough with paranoia, he will kill everyone else for being possessed. Make him possessed, and he'll kill himself. Then push some pilgrims in and do it all again.
If you got bored, you could go to a time period and get missions to go to places in the sandbox place and kill something or other. It would have tons of weapons, spells, and things to ride on and it wouldn't have a leveling system. It's just that some monsters are harder to kill without getting certain weapons. And to get certain weapons, you have to kill certain monsters or buy from certain people. You can keep one weapon from any time period to the next.
This would have Fallout-type consequences. Put all your points into one skill, your other skills will have a lack and you will be unlikeable. You don't get points from leveling up, you are given points from doing quests.
