Spiral
A universal / setting agnostic, percentile based system.
https://thealeks.itch.io/spiral
The summary more or less says it all. Spiral is probably my biggest (it's an actual "book" at 175 pages) and crunchiest (although that's not saying much) game and is basically "yet another" universal tabletop rpg system that one can use to play all sorts of campaigns. It's designed to be flexible and accessible, and is kind of what would happen if the Cypher System and BRP had a baby together, I guess?