Slaves to Armok II: Dwarf Fortress

"Slaves to Armok: God of Blood Chapter II: Dwarf Fortress (Dwarf Fortress for short) is a freeware computer game by Bay 12 Games for Microsoft Windows, Linux, and Mac OS X set in a high fantasy universe that combines aspects of roguelike and city-building games. The title of the game is inspired by its primary focus on the construction, management, and exploration of dwarven fortresses within the game world.

The game offers two play modes: "Dwarf Fortress" mode, in which the player builds a dwarven settlement, and "Adventurer" mode, in which the player controls a single character in a generally roguelike manner. Only one mode at a time can be actively played in a given game world, although adventurers can visit abandoned or demolished fortresses built in prior games.

The game difficulty is variable, but its slant towards difficulty is reflected in the game's motto, "Losing is Fun". The first few attempts for newer players can often end in disaster. However, as time progresses, and the user's fortress grows, the game presents fewer late-game challenges."

Source: Wikipedia, "Dwarf_Fortress," available under the CC-BY-SA License.