Mutants & Masterminds has a damage save system. You don't have hit points; when you get hit, you make a damage save (based on Constitution) and if you fail, you can take penalties up to and including being stunned. As far as I can tell, taking immunity to stun mitigates many of these penalties, but it costs a lot, and you'll still be taking other penalties. (A low-level "Batman" game would have no one with that attribute. I've never seen anyone take it, but if I play another M&M character, I'll try one so I can be an unstoppable Terminator.)
The math is complex, preventing me from going into further detail.
FATE has "stress" and "consequences". You get 3-5 (depending on which version) physical and mental stress, though these can be raised passively with Endurance and Resolve, respectively (by 1 point per 2 ranks, max 5 ranks). Stress stacks up in a weird way, similar to M&M, although it's easier; if I could draw a diagram here I could have shown it to you. If you take more stress than you have stress boxes (generally caused by rolling over; attacks do very little damage in this system) you can suffer a consequence, ranging from minor ("sprain" or "bruise") to severe ("sword in the lungs"). When you have a consequence, an enemy can treat it like an aspect, getting a +2 bonus to a check against you (or getting to reroll a check against you), kind of like combat advantage. You can have multiple consequences, but only 1 of each of the four grades. After a battle, all stress and minor consequences heal up. Others require time and a plot-related explanation (eg surgery). It's actually pretty hard to suffer anything but a minor consequence, and you can voluntarily take another type of consequence to reduce an injury level (eg throwing your arm in the way, so the wound to your gut isn't quite as nasty, but now people can take advantage of your injured arm).
Raising skills (including Endurance) is very difficult; I'm not even sure if the core rules allow for this. Raising a skill where you already have a high rank is nearly impossible.
GURPS causes you to take penalties to your Health depending on how hard you were hit. Once that's gone, you take penalties to other stats (eg Agility), which will seriously mess you up. I don't know how healing works in GURPS, but most settings don't seem to have much in the way of non-scientific healing, which means you'll be hurting a long time. Armor resists damage.
Alternity does have hit points (stun/wound/mortal/fatigue points), the first two equal to your Con and the latter two equal to half that (though you can buy with advances; note that it's a low power system and buying multiple advances is extremely difficult). Hit points, in other words, do not automatically increase with levels. An Amazing hit (basically a critical hit) usually does damage straight to mortal points, and weapons of Good or Amazing quality (like a starship weapon) do the same thing. Most starship weapons do "stun" damage (which is pretty weak in spaceship combat, which takes a long time, but will be doing a decent amount of mortal damage to a, well, mortal. Why a spaceship is shooting at a person is a question for another time.)
Heroic characters get an average 10 per stat (the same six as in D&D, but Wisdom is Will and Charisma is Personality). A soldier might have a Con of 12, so 12/12/6/6 is a pretty common figure.
Armor resists damage, and the best way to avoid being hit is to build up your "resistance modifiers" (very roughly equal to a stat bonus to AC). Being a Free Agent gives you a free 1 step modifier to a resistance modifier of your choice, but Combat Specialists get a 1 step bonus to an attack skill of their choice, so it can match out. Acrobatics-dodge can give you bigger resistance bonuses, but at a cost of a penalty to attack skill checks. Cover increases resistance modifiers too. (If your character had a Dex of 13 [+2 resistance modifier] and got a good result on Acrobatics-doge [another +2 modifier] and threw themself behind a hedge [another +1 resist modifier] you could enjoy a +5 step modifier, which means the enemy is taking a -d20 penalty to their attack roll, although the Free Agent will be taking a 1 step penalty [+d4] to hit. However, a combat spec shooting at you with a rifle at close range [-1 step bonus for combat spec, -1 step bonus for using a rifle at close range] can mitigate that, even further with a "short burst" [another -1 step bonus] and a laser pointer [yet another -1 step bonus], so now they're only taking a +1 step penalty, which is a +d4 penalty to the attack roll.)
If you lose half or more of your stun or wound points, you take a 1 step penalty to all actions (cumulative). The penalty is 1 step per point of mortal and fatigue damage, so even a character who bought up extra mortal boxes is still hosed if they take any mortal damage, it just means they get to crawl away and live. Probably.
Healing is very weak.
Damage "leaks". If you were wearing a tactical vest (1d6-1 resist vs high impact attacks, which is another way of saying ballistic), and someone shot you for 4 points of wounds with a shotgun, you might roll high enough to resist all the incoming damage, but you still take half of that (in stun) from the shotgun, which the armor will not prevent. Things get weird if you're taking stun damage (from say a shock baton) and wound damage from another source.
It gets weird if you allow sci-fi (eg a Progress Level of 6+) or FX (magic, psionics, etc). For instance, powered armor (PL 6) gives you Good toughness (like a vehicle), and a Deflection Inducer could give you free resistance bonuses. Most forms of magic do not ignore armor, along with psychokinetic attacks, but telepathic attacks bypass armor completely -- though they do low damage -- and are resisted by the Will resistance modifier, which combat characters usually neglect. The tire telepathic power does 1 point of fatigue damage per point of success (Ordinary/Good/Amazing) which can easily cripple an enemy fast, even if you can't tap out their fatigue pool. Also, the weren race gets 1.5 times the expected points in stun/wound/mortal/fatigue. While having more mortal and fatigue doesn't do much
I suppose I should ask, what, exactly, are you looking for? Did you want combat to be deadly? Did you want the consequences of combat to be deadly? They're not the same thing! (IMO, deadly combat is good, deadly consequences are not. Once the battle is over, I have no problem with fast non-scientific healing.)
An example of a system that didn't work is A Song of Ice and Fire, which is the worst of both worlds. It's not even realistic in terms of the damage your character can take, but is relentlessly realistic in terms of how long it takes to recover. My own character, a stealthy social type (a spy, basically) with virtually no combat skill easily survived an assassination attempt by a character with a dagger. He only took 2 damage (-1 for leather armor), out of his possible 9 points. The DM joked he should have used a peasant with a farming implement, since two-handed weapons deal high damage.) In an earlier battle, our knight basically solo'd four archers (which do high damage) by himself, taking injuries (letting you subtract damage from an attack for a -1 universal penalty) and wounds (same but a - 2 penalty). He had to take a long route (it was a mountain) through difficult terrain, but he massacred the archers. However, wounds take so long to heal he was out of commission for a week, and it actually took longer since we had to move him by horse. My own character took 0 damage that battle, through the act of rushing a big angry guy and fighting defensively until the archers were inevitably killed, at which point the rest of the party could rescue him.
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