I have a scenario that I worked up called "The Dying World", in a nutshell 50% of all living things die, and reanimate do to a new infectious microbe/amoeba. The remaining living 30% have a minor change either positive or negative, 10% get a new psychic abilite, 10% remain immune. As the game progresses zombies evolve more aspects, and some of the living become psychically or magically enabled.

An off the cuff idea:
A deadworld setting where players start in a future where mankind has had to abandon earth and lives in a small orbiting space station.  Time travel is developed with players going on missions back in time, but the technology only works if a time-warp repeater is built in each era. Forcing players to go back into time in reverse chronological order to stop key areas and to create new future opportunities. 

So for instance you have to do a sci-fi game in a near future to try and save a few extra people on the last shuttle launch go back to the future and more people have survived (with its own repercussions)
Go back to the modern area to help hold back the destruction of a last bastion on earth,
etc, until you go way back to ancient china or the dark ages and stop the first isolated outbreak that all future zombifications come from....

There could be 2 final endings.  Players succeed and dissolve as thier timeline no longer exists, or while they are trying to destroy the original source they accidently leave behind something that actually causes the whole outbreaks to intensify and close a time loop where the go back to the last fragments of humanity stuck on a space station and all there work has been undone.

RPGs I am currently into: >>>All Flesh Must Be Eaten, Conspiracy X, Paranoia XP, Interface Zero, Realms of Cthulhu, Abandon All Hope, Dark Heresy<<<
My 40k Armies and Model lists >>>Hive Fleet Mantid, Space Marines Ashen Lions Chapter <<<
Last Edited By: DemoRic Oct 11 14 6:45 AM. Edited 1 times.