I remember from the old forum that a user named Eairle suggested a sandbox thing that emulated the lore of "Autumn." They haven't come back since, and I'm reviving it since I thought it was neat and wanted to continue any discussion on the topic. A disease kills a tremendous number of the population, and a portion of those who died revived after a while and started walking about. They begin fairly senseless and slow, but become progressively faster and more intelligent as their bodies begin to crumble. Lots of still corpses everywhere, and practically no danger in the first week of play, but quickly gets more and more dangerous as they get more sensitive and cognitive with time.