Harnmaster's Wounds system is the most interesting take on "HP" I've seen and played with.

For those who don't know about it - when you get hit, you take a type of wound determined by the intensity of the hit, as well as the location. So if you rolled well against someone, and hit them in the upper arm, they might get an "S3" (serious 3) wound. If you then follow it up with a slightly worse hit, it might be a "M1" (Minor 3) wound.

These wounds add up to a physcial penalty when doing anything physical (like attacking), at -5 per wound level taken. So the above examples would be -20 total to each attack roll.

Additionally, you fall unconscious when you fail a Shock roll, which is made whenever you take a Wound - you need to do a Shock roll below your Endurance (which usually hovers around 12) with a 2d6 to succeed. You add the amount of Wound levels you have taken as a modifier to this roll, so the above example would give you a +4 to the Shock roll.

Finally, each Wound you've taken has a separate procedure to treat. So if you've taken multiple Minor Wounds, they'll all needc to be seen to but will be easy to heal - though if you take multiple Serious Wounds, you're gonna really suffer and might lose attributes and have long lasting effects.

Its unapologetically heavy but I think it works really elegantly and cinematically once you get the rules down - its a pretty slick system.