Left for Dead has robust AI. It is made so that a scenario can be played over and over again with different layouts of computer players. The design of the zom

Left for Dead has robust AI. It is made so that a scenario can be played over and over again with different layouts of computer players. The design of the zombies requires teamwork. I believe the key to the fun of that game is in the single player is the AI. Without good AI it would be no fun at all. It is not open source but I did see a presentation about its pathing on the internet.