One, Tiny Frontiers, is a drastically simplified 2D6 game. And when I say simplified, I mean “all weapons deal the same damage” and “all members of a race have the same hit points” simplified.
On the other hand, if you just want to get a game up fast for people new to RPGs who want to get straight to the action, it’s a useful thing ruleset to have.
On the other side, there is Planet Mercenary. Based off of the Schlock Mercenary comic, it’s a game system that grounded in fun and fast action. I do like the “speak first, act first” rule, as it gets things going fast, and the mercenary cards mechanic adds a certain flavor to the role-playing.
It isn’t really suitable for me and my near-grimdark perspective on mercenaries, but its basically entertainment, and there should be a place for simple wild adventure on the battlefield.
Both games have interesting settings: Tiny Frontiers have a host of quick-n-odd settings, sketched out for a few pages, while Planet Mercenary has an elaborate detailed setting that – despite its comic origins – give more than a few nods to reality (something that I appreciate.)