What is Zombie Panic: Source?

Zombie Panic: Source is an extremely fun mod in which you are playing either as a human or a zombie. If you are a zombie, you work best in numbers. While you do have to use teamwork while you are a human, your goal is to either survive or a newer objective version of the game. You can now download Zombie Panic: Source on steam! For more information about the game, just go to the link to the website below.