GTA: Trucking Zombies
No one like it, but it did happened, it was the end of the world as zombies began appearing. Soon, everyone that you know become infected. Fortunately, you are able to find two allies. You and your friends decided to escape the city. Gun down every zombies that you see following you. When you run out of bullets, you can always switch to another character. Each zombie kills earns you money. You can use the money to upgrade your weapon of choice. The game would be harder as you make some progress, so you need the upgrades.