Cataclysm: Dark Days Ahead (CDDA) is an open-source survival horror roguelike video game.

At game start, the player has multiple approaches, including things required for day-to-day survival such as scavenging, hunting, and finding shelter, as well as larger goals such as farming, installing bionics, making and repairing vehicles, and constructing homes.

The game is set in New England[7] in 2026 (current year + 1), after a catastrophic event killed most of the human population and spawned various monsters and hazards.

In their explorations they obtained a sample called XE-037 (known within developers as The Blob) that was able to reanimate the dead and cause targeted phenotype mutations.

[9] Though the cataclysm is predominantly a zombie apocalypse, many other apocalyptic events are occurring alongside it, including invasions from fungi, Triffids, and Lovecraftian monsters such as Mi-Gos that have built encampments and towers around the world.

[15] In December 2015, an unofficial launcher was created for CDDA under an open-source MIT license to allow players to stay up to date with the latest releases and third-party mods.

[20] Unlike most roguelikes, the game features non-linear gameplay: the player is free to explore the procedurally generated map, clear areas of monsters, work with NPCs, and build shelters and vehicles.

The gameplay is mainly based on day-to-day survival, and the game tracks parameters like hunger, thirst, morale, illness and temperature which the player must manage to stay alive.

The game also manages numerous other mechanics about the player including drug addiction, mutations, broken limbs, and bionic implants.

Cities and towns generally have several common establishments often found in the real world such as houses, stores, malls, parking lots, swimming pools, hospitals, and more, but hold danger in the form of large hordes.

Despite the game lean toward looting as primary source of tools and equipment, CDDA has a detailed crafting system, with many basic necessities such as clothing and food being craftable from raw items that are found lying around the world.

Crafting can be hampered by player conditions such as low morale, damaged limbs, insufficient light or lack of flat surface or workbench.

For the most part, the terrain in the game is fully destructible, meaning that the player and other entities can destroy it or build structures on it.

Players are reported to have created vehicles of quite different sizes and capabilities, from small quad bikes with limited storage[24] to huge "deathmobiles"[25] with multiple engines, turrets, machine guns, and chemical labs.

The player can farm land and grow grains, vegetables, berries and other shrubs (e.g. cotton), provided that they find the respective seeds.

Mundane animals may be replaced with zombie or mutant versions, further reducing access to edible meat while making the world more hostile.