Dwarf Fortress is an entirely too addictive SimulationGame coded almost singlehandedly by Tarn "Toady One" Adams and his brother Zach "Three Toes" Adams. Imagine if you would, TheSims. Except that instead of a yuppie family, you're guiding dwarves who are staking a claim in the wild frontier. Take out the need for one bathroom for every simulated person and add in the need to drink booze constantly. Take away the cute mental breakdowns with the kooky psychiatrist and replace it with tantrums and moods where your dwarf will decide to start hacking down everyone around him, or maybe just kill one nearby dwarf and make leather armor out of their skin. Oh, and did I mention that you can't directly control the dwarfs, but rather you assign them a range of duties and their AI decides whether they'd rather be Cleaning, doing Masonry, or going Fishing?

'''Notable aspects'''
* PoorUserInterfaceDesign - There are two different ways to scroll through menus. Only one will work on any given menu. The other will force you to lose focus on the object you were viewing. Almost every letter does something on the main menu. Some of the functions are actually listed. 
* RogueLike - the graphics for the game are done using a slightly bastardized version of Code Page 437. This means that every creature, every item, every bit of terrain, is indicated through the use of ASCII characters. Whether this is a plus or a minus for the game depends on who you ask and how much they enjoyed NetHack. No, the dwarves are neither represented by AtSigns or the letter D. 
* UserCommunity - The game has a vibrant user community including a wiki that covers almost every aspect of the game and is constantly updated as people learn new tricks. Which is good because...
* InsufficientDocumentation - The game has a minimal set of documentation that comes with the game which barely describes the interface and a few basic concepts. There is no tutorial level. There is no information in-game on what needs to be done to create a successful settlement. Heck, the game doesn't even tell you what your goal is (survival, as well as any incidental fun goals you feel like adding in). There are any number of ways for your Dwarves to die horrible and entertaining deaths from goblin sieges to lava floods to rampaging elephants to deadly carp to winter starvation to mass hysterical slaughter to... did we mention that one of the mottos of the game is the LosingIsFun?
* SandboxGame - Theoretically, the goal is survival. However, most players quickly start their own little subgoals from trying to optimize their fortress to developing an 80-story statue of the founding dwarf. Then, there are the people building simple computers using the hydrodynamics system of the game...
* EditableRaws - Most of the data in the game is stored as PlainText files. The player is free to add new races, modify the language grammar, create thermonuclear catsplosions (setting the temperature of cats to a few million degrees results in a rather impressive fireball consuming the known world).
* PlayByMail - Not natively supported, but the game saves are very compact, so it's not uncommon for players to do a "Succession Game" where the game is handed off to another player on the list at the end of an in-game year with amusing descriptions of the happenings of the year posted on the Internet, using in an in-genre style.
* CrazyDetail - There is a full-blown weather and erosion simulation in place to generate the worlds. Several centuries of history are generated including the rise and fall of civilizations and the results of battles involving heroes. This history has a direct impact on the world that you start in and more detailed accounts are uncovered as the game is played and artifacts found.
* SingleDevelopers - Tarn has always done the majority of the coding on the project. He's being a bit more successful than DerekSmart at not getting bogged down in the details and failing to release a workable game.

'''Links'''

Official website: http://www.bay12games.com/dwarves/index.html
* Wiki (pretty much essential if you want to get anywhere): http://www.dwarffortresswiki.net/index.php/Main_Page