Four Bookmooch books today:

Year Zero by Jeff Long - two thousand year old plague unleashed on the world.
Plague Year by Jeff Carlson - Nanotechnology evolves into a machine plague which wipes out 5 billion people.
The Rift by Walter J. Williams - Massive earthquake causes a rift across America.

(Notice a theme!?)

And finally:

Beauty by Sheri S. Tepper - A sort of time travel, fantasy fairy tale. Looks super.