For quite a long time now I've been toying with the idea of going through the old AD&D World Builder's Guide (good luck finding it legally, since Hasbro killed off all digital sales of previous versions of the game) and building a world from the top down. Since it's old school D&D, there's random tables for every step of the way, from cosmology and world shape all the way down to individual cities, and half the fun of those things is trying to justify the results they give.
I thought it might be fun to make it a collaborative effort. Every few days, I'd roll some dice, post the result (or results, with groups of related tables), and then let people suggest an explanation. Some steps might not need much of one, but we can always just take a result and move on to the next one if something like that comes up.
So for starters, I've rolled twice on the World Hooks table to come up with a general theme for the setting, and come up with Situational: Psionics and Historical: Migration. So mental powers abound in a land that's experiencing a mass migration of various peoples (like Iron Age and early medieval Europe). Could be due to the collapse of an earlier empire, or some psychic catastrophe.