What if everyone started living the same day over and over again, but, unlike most situations, everyone knew about it?
I’ve adapted this marvelous idea slightly:
On August 10, 2008 at 2:39 am GMT, the universe reverts to the state it was in on August 8 at 9:28 pm GMT. Then on August 10, it happens again. And again. The universe is stuck in time loop that lasts 29 hours 11 minutes. Only one thing transcends the resets: consciousness. People retain their memories through the time loops.
That’s nearly all I have to start with. I currently have no plot and no characters. I do have a scene or two in mind to get my fingers moving. And I’m starting to flesh out some of the social, political, scientific, and religious implications of the time loop. All of that speculation has yet to yield a single plot idea, but this is NaNoWriMo, so it’s okay if I have no idea what happens next.