I believe War Z was spun off of Day Z, as Day Z is a mod that is very limited by it's engine at the moment.
I can highly recommend DayZ Good times [video=youtube;d2LB2GhHlmI]http://www.youtube.com/watch?v=d2LB2GhHlmI&feature=player_embedded[/video] I heared there was quite a problem with hackers but if you play on a private hive you should be fine