This is almost certainly the lightest weight osr game I've seen. It fits on a page, and there's no bestiary or adventure or anything to go with it, but it has a ton of cool mechanical flourishes.
Skills are pick-or-invent-your-own, attributes are randomly distributed but you'll never have more or less than another player, attack is heavily weighted towards hitting, and there's two HP bars (flesh and grip.)
Per the page description, it's an abandoned project, but I'm intrigued and I'd love to see the new version of the game when it's released.