I've read a bunch of community forts, but alas, my computer just isn't good enough to handle them - the one time I tried, I was two or three overseers in and had no more than a dozen FPS. An idea struck me the other night, though.
The dwarves arrive to an empty fortress, dug out but with nothing inside. Clearly someone lived here - briefly, perhaps - but nobody is there anymore. Nothing, not even bodies - just restless spirits. Between overseers, the save gets passed back to me - and I perform some select modding to up the difficulty. Anything from making picks unable to mine for a year to increasing the size of goblins, making a trade partner hostile, unleashing a plague or bringing in new invaders - I'm familiar enough with modding that I can probably do all of those, although I would have to prep the scene before generating the world.
Why would I do this, though? Because I'm not playing as the dwarves. I'm playing as the angry earth, the devouring thing in the darkness that consumed the previous inhabitants.
If you think this is a good idea, go ahead and post - and perhaps suggest more ways to mess with the poor dorfs. One catch is that nothing I do should require me to ever actually start the game (except to test the results of my tinkering - making sure it results in !Fun! rather than an instant game over).