Excellent mini novella by Jack London in 1912, about a plague that wipes out most of humanity in 2013. Good guess at eight billion world population.
Has elements of EARTH ABIDES in it and some echoes of notions about cyclic nature of civilizations.
I happen to stumble over it while gathering free books to put onto my super mega reference CD for Vault-OS. Strangely enough, you can easily fit 1000's of free books into less memory than is taken up by a few PDF files.