Grab your pickaxe and secure your book of procedurally-generated poetry, because Dwarf Fortress is out on Steam right, flipping, now. Bay 12 Games's hugely ambitious colony sim, which is notionally a game about building a fortress for small, bearded humanoids, but is really an engine for generating elaborate fantasy histories and player-driven stories within them, has been in active development since 2003, with an initial launch in 2006. Since then, it has been continually developed by brothers Tarn and Zach Adams, who have added a truly wild amount of stuff over the last two decades. It's also famously as impenetrable as its title suggests, mainly due to its ASCII visuals and unwieldy, keyboard-exclusive control scheme.
