Dwarf Fortress is a roguelike-inspired fantasy world simulator. That is, it procedurally generates a whole world with civilizations, monsters, religions, instruments, individuals, wars and history et cetera et cetera. The player then interacts with this world. There are two game modes, but it is most known for fortress mode in which the player directs a starting population of seven dwarves to inhabit a small area of the world and do whatever. You could say it's akin to Minecraft in that sense, which has cited DF as an influence.

DF has been in development for 13 years continuously, programmed by one person who does this full time via donations. He has said it will be his life's work. It's remarkable for it's unparalleled depth. For example, DF is anatomically detailed down to bones cartilage and nervous tissue, and combat between two creatures is a simulation of the material properties of the weapon being used against said organs and parts. That sort of depth is present in pretty much every facet of the game. Oh, and it's in ASCII. Currently, alpha version 0.47.01 is out.

OH BOY.

Dwarf Fortress is barely a blip on the mainstream radar, but it’s an object of intense cult adoration. Its various versions have been downloaded in the neighborhood of a million times, although the number of players who have persisted past an initial attempt is doubtless much smaller. As with popular simulation games like the Sims series, in which players control households, or the Facebook fad FarmVille, where they tend crops, players in Dwarf Fortress are responsible for the cultivation and management of a virtual ecosystem — in this case, a colony of dwarves trying to build a thriving fortress in a randomly generated world. Unlike those games, though, Dwarf Fortress unfolds as a series of staggeringly elaborate challenges and devastating setbacks that lead, no matter how well one plays, to eventual ruin. The goal, in the game’s main mode, is to build as much and as imaginatively as possible before some calamity — stampeding elephants, famine, vampire dwarves — wipes you out for good...Dwarf Fortress may not look real, but once you’re hooked, it feels vast, enveloping, alive. To control your world, you toggle between multiple menus of text commands; seemingly simple acts like planting crops and forging weapons require involved choices about soil and season and smelting and ores. A micromanager’s dream, the game gleefully blurs the distinction between painstaking labor and creative thrill.

- NYT

Here's a comment I left about it:

Dwarf fortress is complex and challenging to master. The pursuit of mastery is why I keep coming back to it - there's so much to do, to see, to create. It's a massive, spiraling game and discovering what it has to offer brings me stupid amounts of entertainment. My first fortress was a hovel of dwarves eating planted mushrooms in a bloodsoaked dining hall made of dirt. My most recent fortresses have hundreds of citizens, living in marble bedrooms and drinking from golden goblets. I learned how to play, and it opened up other avenues for mechanical exploration. Recently, I've started a fortress defended entirely with ballista towers instead of a traditional military.

It's my favorite game of all time (at the moment), and I hope to keep playing it for years.

Here's one of my favorite bugs that rose from the complexity of the simple systems comprising the game's whole:

I added taverns to fortress mode, so the dwarves will go to a proper establishment, get mugs, and make orders, and they’ll drink in the mug. And, you know, things happen, mugs get spilled, there’s some alcohol on the ground.

Now, the cats would walk into the taverns, right, and because of the old blood footprint code from, like, eight years ago or something, they would get alcohol on their feet. It was originally so people could pad blood around, but now any liquid, right, so they get alcohol on their feet. And then I wanted to add cleaning stuff so when people were bathing, or I even made eyelids work for no reason, because I do random things sometimes. So cats will lick and clean themselves, and on a lark, when I made them clean themselves I’m like, ‘Well, it’s a cat. When you do lick cleaning, you actually ingest the thing that you’re cleaning off, right? They make hairballs, so they must swallow something, right?' And so the cats, when they cleaned the alcohol off their feet, they all got drunk. Because they were drinking.

But the numbers were off on that. I had never thought about, you know, activating inebriation syndromes back when I was adding the cleaning stuff. I was just like, ‘Well, they ingest it and they get a full dose,’ but a full dose is a whole mug of alcohol for a cat-sized creature, and it does all the blood alcohol size-based calculations, so the cats would get sick and vomit all over the tavern.

- Tarn Adams, co-creator of DF

Dwarf Fortress is awesome.

I am terrible at it.

This story is hilarious.

https://lparchive.org/Dwarf-Fortress-Boatmurdered/Introduction/