Zed or Alive is a set of free wargames rules for Zombie Apocalypse skirmishes. To play, you’ll also need a copy of Savage Worlds Showdown (also free). The authors write:

Zed or Alive is a campaign-based miniatures skirmish game using the award-winning Savage Worlds: Showdown! system set in the years following the zombie apocalypse. You control one of several human group types such as Survivors, Tribals, or Military and battle each other and the ever-present zombie menace to gain weapons, supplies, and dominance!
Alternately, you may choose to play as a Virus Strain, gaining evolutionary material with every battle and evolving to become increasingly lethal!
This PDF rulebook provides players with a fast, furious, and fun miniatures game that allows them to use any zombie or survivor figures to play out campaigns just like your favorite zombie movies and shows!