Valve has announced that the latest major downloadable content (DLC) update for its co-operative zombie thriller Left 4 Dead (L4D) is now available, free of charge, for PC and Xbox 360. Entitled "Crash Course", this DLC delivers new single-player, multiplayer and co-operative gameplay to both platforms. Crash Course bridges the gap between the end of the "No Mercy" campaign and the beginning of "Death Toll" in the original game, expanding the game universe with new locations, new dialogue from the original cast, and an explosive finale.