While Project Zomboid players scavenge for supplies and complete unique quests, an NPC will be nearby doing the exact same things.
Before DayZ and State of Decay arrived on the scene, The Indie Stone's Project Zomboid was the zombie apocalypse simulator to get excited about. The current build is only available as a playable alpha, thanks in part to various unforeseen setbacks, but it's managed to attract a loyal fanbase with complex survival gameplay and modding capabilities. An official release is still on the way, but apocalypse-simulators have become a lot more common since Project Zomboid was first announced. The Indie Stone happens to have a few new tricks up its sleeve though, including a meta-game system that will be introduced in a future patch. Once added, this system will make NPCs practically equal to player characters in every way; while you're struggling against the zombie horde on one corner of the map, an NPC will be somewhere else having an adventure of its very own.
Under the meta-game system, NPCs can be programmed with scripted stories that unfold in real-time. Meta-game characters will engage each other in conversations, forage for quest-specific items, and even attempt to fight off the undead. Each story will unfold without any player involvement, while encounter outcomes are generated using set probabilities and predetermined character traits. This also means that identical meta-stories could end in different ways for each playthrough. By the time players finally reach an NPC, it could have been eaten by zombies, shot by raiders, or burned down in its shelter by an out-of-control cooking fire.
Once the feature is live, Project Zomboid meta-games will be available in Survival mode, while Sandbox and Last Stand modes remain more or less the same. As with other game features, modders will have the ability to expand on existing meta-stories, or create their own from scratch. Sure, each meta-story will likely be prone to bugs, while 75% of the plots will be pulled directly from The Walking Dead. On the whole though, this should give each Project Zomboid playthrough a uniquely organic game world, and that's a very interesting prospect.
Source: Project Zomboid