Cataclysm DDA is a survival roguelike that takes place in an alternate future where the world has ended in multiple different ways. There are the main threats in cities, which are the zombies (including optional special infecteds), but also includes giant blobs, triffids, mutants, giant ants/insects, nether-spawn, spooky labs to explore, and more. One of the biggest draws of the game is it's huge crafting system and in-depth vehicle construction system, with close to a thousand crafting recipes not including optional content.
To start, the game boasts a huge amount of options for character creation, such as positive/negative traits, classic roguelike attributes, and skills in a plethora of areas. There are also loads of scenarios to choose from, professions to choose, from, and a huge list of optional content and the ability to blacklist pretty much everything that is not to your liking. You begin in a small building on the outskirts of a city (depending on your chosen scenario) and must survive however you see fit.
Pics:
My current character


Pics from the website


I very strongly recommend you use the newest experimental builds to play as the newest stable build has not been updated in around 2 years and in missing loads of content. If you don't feel like updating the game every time a new nightly comes out, there is a launcher available that will do it for you: http://smf.cataclysmdda.com/index.php?topic=11895.0
Game link: http://en.cataclysmdda.com/