Z-Day, in spite of its title, is not trying to copy DayZ. This Far Cry 3 mod has plenty of zombies in it but it's not another multiplayer survival game.
"The campaign will consist of multiple singleplayer missions very much inspired by games like Left4Dead, but with a Far Cry twist to them," creator GC Vos says on Z-Day's ModDB page. "The maps are all built from the ground up using assets at hand. Z-DAY will not merely be a bunch of maps or a mod alone though. It's as close to a completely new game as you can get. The campaign will include an immersive soundtrack, cinematic cutscenes, custom sound effects and voiceover work."
In the first seven minutes of gameplay, the player must get to the supermarket for food. They have a pistol but they're greatly outnumbered by zombified humans and animals. They have to sneak through buildings and across rooftops without drawing any attention. They can mark enemies to keep track of their location.
Like Far Cry 3, Z-Day features drivable vehicles. A gameplay teaser shows the player character driving a jeep across a highway. They weave back and forth between wrecked vehicles and steamroll any zombies in their path.
While GC Vos says that the game is inspired by Left 4 Dead, it reminds me more of FC3. It seems to retain the best aspect of that game: the seamless mix of gunfights, stealth and vehicles. You won't have a huge world to explore but the player still has plenty of choices in how to proceed through each level.
GC Vos realizes that Z-Day's name is "too similar to other titles." The team is planning to reveal a new name for the mod very soon. This will require them to change several assets for the game, though, so it's going to take them a little time.
The open beta for Z-Day will launch on March 1st. The developers expect to officially release the mod this summer.