The Gaming Den

Per the subject line, what core system/engine is best for replicating mundane humans in modern day, presuming no supernatural elements or high science?

Do I use d20 with different skills? Shadowrun/After Sundown with the magic/matrix/cyber ripped out? GURPS? Spawn of Fashan homebrew?

Honestly, FATE works pretty well for this. Maybe with an abbreviated skill pyramid for most people (most people probably have a single "Good/+3" skill, at best, then two "Fair/+2" and three "Average/+1"), and then people who are remarkable in their field get the standard FATE pyramid (another skill of each category, and a single "Great/+4" skill).

FATE has no one assumed genre, and can handle mundane pretty well, and Stunts can easily be entirely non-supernatural. Maybe they're, like, Hollywood mundane, but still. It can be things like "Fast Talking: You can use Deceive in place of Contacts" for a character who's good at fast talking and convincing people they already know them.

What genre are you looking for? "Action movie" mundane or "soap opera" mundane? Or something else entirely?

After Sundown's approach to the mundane is mostly: rely on your real-world experience to estimate DCs, and also have a comedy of errors due to the dicepool system. You'd probably have to increase the dice pool size of mundane people a bit (and tweak combat to compensate) because dice pools have a sweet spot.

3.5e D&D's is: have a detailed set of DCs for things an athletic person might want to do in a dungeon or cave, paving the way for potentially having you write DCs for all sorts of other skills. Also the combat system needs you to write new classes or things get really odd past level 3.

Cybergems (Gempunks but cyber instead of magic, but then you remove the cyber) is: you can play as Bruce Willis, Jason Statham, Bruce Willis's hacker sidekick, or a squad of goons in black vans, and gunfights while standing on fighter jets. Not much emulation of navigating the DMV though.

Narrative games like Fate or Munchausen or Lasers & Feelings can of course emulate every setting with equal grace.

Genre is roughly police procedural

I feel like that horror/despair resolve system being discussed in another thread could be attached to a lite FATE or Munchausen thing to create a horror game

Kurosawa would rent a comfy inn for his writing team and they'd just go over a scenario together.