One of the things that I think draws people in to challenges is just the "rules" that go into them allowing us to have dramatically different universes and playstyles in our games. But challenges usually seem to have a defined "end" where you've either won or lost the challenge, and part of what makes the Sims games so engaging is the open-ended opportunities there! So, what sets of rules would you set up to create different "universes" in your games, where you're not working towards a specific result, just directing your Sims' lives in a new direction?

For example, I just finished re-reading the Bartimaeus Trilogy by Jonathan Stroud, and I think it would be pretty easy to approximate that universe within TS2, and then just allow your game to progress from there like you would any other story. You'd just start with rules like these:

-Society is divided into Magicians (witches and warlocks) and Commoners (non-witches)
-Only Magicians can use any "magical" items (including career and aspiration rewards)
-Only Magicians can have "government" jobs (politics, law, intelligence, etc.) above level 3
-Only Magicians can have ANY job above level 5
-Magicians' magic skill level must be at least as high as their job level.
-Law enforcement Magicians must also be Werewolves.
-Magicians cannot have children of their own, they must adopt any they wish to have
-Only adopted children of Magicians can become Magicians themselves
-Commoners may have biological children
-Commoners may give up children for adoption by Magicians in exchange for a large sum of money (say, $10-20,000)
-Magicians must have "witchiness" as a turn-on, and will not deign to enter into relationships with commoners (or if they do, it will have a Romeo & Juliet- esque "forbidden love" nature)

And once you have general rules like that established, many other elements of the story fall naturally into place, and you're free to develop your own Magical society from there!

So what rules might you put into place to shepherd your game in the direction of other fictional or historic universes?