Cataclysm: Dark Days Ahead (also known as CDDA) is a roguelike open-world survival craft CRPG. It takes place in a dystopian eastern U.S. in the aftermath of a worldwide apocalypse brought about by zombie outbreak, dimensional invasion and biological infestation. The game is quasi-turn-based, in the same manner as games like Dwarf Fortress, and features a pure skill-based character system in the mould of games like Fallout or GURPS.
Started in early 2013, CDDA is a fork of Cataclysm (2010), whose developer, Whales, released the game's source code under open-source license in 2010 and ceased development of the game in 2012. Coordinated by Kevin Granade after a successful Kickstarter campaign to fund full-time development of the game for a time, the game continues to be developed under open-source license by an active development community, with experimental builds being released daily as of this writing on January 28, 2021.
Its design document cites the Ultima series, the Fallout series, the first two X-COM games, and Dwarf Fortress as the game's primary inspirations, and, consequently, the game takes place in a fully-procedurally-generated world with destructible (and buildable) environments; vehicles that can be fully modified, constructed and driven; and NPCs who can become companions.
While CDDA does feature a loose, over-arching plot that ties together the various disasters into a coherent whole, the game is open-ended in format, and the game world can be endlessly extended proceduraly.