1800 hours of playtime and counting. Solo or with friends, this game is a highly customizable experience, both through game-settings and through modding. The atmosphere can be anything from pleasant to tense, as you sneak around sites trying to find useful stuff or complete a mission. Pay attention or pay the price! It is a "sandbox game", in the sense that the game doesn't set any goals for you. You can play singleplayer or set up a server to play either alongside friends or in one or more teams. The name hints at the default setting for the core "gameloop", in which you have 7 days to set up a base, to protect yourself from when a sudden horde of zombies will attack you. Survive and you get another 7 days. You are, by default, immortal as you resurrect shortly after dying, but that fact, and how much you suffer from dying, is customizable.
Get good enough to stay ahead of the threat, or simply set the threat to zero, and you will have time to focus on building something nice for yourself, using a fairly rich set of buildingblocks, furniture, and paint-options. The game also includes a primitive but useful function for powering and wiring up some things, like lights, automatic doors, and autotargeting gunturrets.
Resources can be collected by buying them from traders (no other NPC:s for now), by searching surrounding locations, or by gathering materials and building stuff yourself. The traders offers a set of tasks to complete for rewards, and also buys some of the things you might want to sell.
At the current state (v1.3) it is hinting at some kind of background story, but none actually exists in-game. Low-level modding is fairly easy as long as you are willing to read the guides on Fandom.com, and learn some markup-language-coding in XML. Mid-level modding can be done through trial and error with more poking around in the games XML-files, and learning how to code basic "regular expressions". High-level modding is possible, but beyond my scope at this point.