On Mighty Thews is a pulp sword & sorcery RPG by Simon Carryer, and one of my favorite "modern" (or "narrative") RPGs.
OMT is designed for prepless oneshot games or short campaigns. At the beginning of the game, the players and the GM follow a few simple, engaging, fun steps that create a "setting" for your session (it can be a city, an empire, a continent, or a whole world). This is mostly done by taking turns at drawing a map, one element at a time. The map will be used by the GM as a setting for the adventure, so the players have a chance to put whatever they think will be fun to see in the game. Infested jungle? City of merchants? Ruins in the desert? Draw it to on the map...
It is a "modern" game, meaning that the rules don't aim at recreating physics but at producing a fun, coherent story, and it codifies specific situations where players partake of the GM's narrative authority.
With proactive, creative players, this game is wonderful. I know, I've played it a lot! It is not particularly suited for campaign play (no conventional character development), but it's amazing for one shot, prepless games.
A fun trivia about OMT: Savage Worlds was one of the inspirations for the game, and so some of the OMT dice, wounds, and raise mechanics are immediately familiar to SW players!
OMT is available on drivethru!