>>529186228
Ascent of Ashes. It's on Steam. Basically a Rimworld with Z-level building and combat.
https://www.youtube.com/watch?v=6sQ-LLXmxlw

I tried the open Early Access demo they had a year or so ago when it was available, but everything was too barebones (no combat, just the basic map/building features) to tell if it would be worth anyone's time. They'd definetly need to add way more stuff than the one that they're releasing it with for it to be worthwile, plus moddability.