Valve's latest "mutation" gametype for the Left 4 Dead 2 "The Passing" DLC takes three survivors out of the equation. "Last Man on Earth" is a single-player mode in which the player is the only Survivor left in the world, and must face nothing but Special Infected without the help of other players or even bots. In other words, it might has well have been called "The Player is Murdered Immediately."
Instead of an opportunity to play with developers (since, you know, it's single-player), Valve is encouraging players to record sixty-second clips of gameplay and upload them to YouTube with the tag "L4D2LastSurvivor." If you want to see lots of footage of player characters being torn apart by Special Infected, now you know where to go.