My setting, Scavenger, is godless. Instead philospophical mysticisms based off cruelty, cause and effect, astrology, and other concepts are practiced via ritual, ceremony, and virtues. The underpinning idea of virtue or sacred in my setting is "helping the tribe survive and flourish" while sin is "something that sabotages you or another's ability to survive or flourish without virtuous reason." So, war can be virtuous, but something like genocide, or various crimes petty or large, can be sinful, leading to criminals often trying to frame their crimes as "for the greater good." Ancestors and culture heroes take the places of messiahs and saints; divination and supernatural ideas are thought of as natural processes, even if ill understood. This set up allows me to mimic anything traditional religions come with.
The three core mysticisms in Scavenger are some of the things Im most proud of as an artist in creating. I can dm you a copy if you'd like!