Alea Iacta Est

Those of you familiar with the d20 Star Wars, Stargate, Spycraft, Farscape or any of a number of others (including Unearthed Arcana for D&D), this system should be old news. However, the version I like to use is a little different to the UA version and most of the others (since the others don't have undead, for a start), so it is still worth reading through this document.

Why?

Lots of reasons.

Description: The idea of hit points as pure attrition in the face of physical damage is absurd, and the homogenous nature of hit points as they stand does much to encourage this. That a 10th level fighter is literally 10 times [actually more] as hardy as a 1st level one, when both are the same race, is crazy. Vitality (a proper description follows) is a far better mechanic for supporting a convincing and heroic-feeling description of the d20 injury system.

Danger: Tension in combat generally arrives quite late, as hit points run low, or when the Ref has hideously stacked the fight and there are one-hit-killers around. When each hit has an element of danger, players are encouraged to fight smarter and the whole game gets more interesting.

Recovery: Vitality recovers much quicker than hit points, allowing for the party to be back on its feet sooner, and reducing the awful dragging feeling you get when you've started the sixth encounter in a row on half health, because the party is out of healing.

Pacing: This variant makes creatures last longer when they would normally be routinely killed in one hit, but it makes tough enemies (and characters) easier to kill. For PCs I counterbalance this by increasing the amount of time available for a healer to get to a dying comrade, meaning that combat death will be very unlikely unless you manage to get knocked down surrounded by enemies, or a very long way from the party.

Rules

The basics of the system follow. These will be fleshed out later, when I get some time to sit down with the book, and may be formalised in a decent article on my web site. Although I currently can't quote specific differences (healing spells being the only one I can think of), this system may not be exactly the same as the UA version.

Vitality points are much like hit points as many people describe them. They represent that heroic knack that characters in fantasy fiction tend to have for avoiding serious injury, by exerting themselves to turn square hits into glancing blows (sometimes avoiding them altogether) and the like.
Wound points are your core physical well-being. Once you begin to lose wounds you are in a sorry state; the pain of any real injury distracts from virtually everything you do, while some injuries will impair your movement, coordination or senses.

Each character gains a die of vitality for each level, and adds their Constitution modifier: your vitality in the new system is equal to your previous hit point total. You have a number of wound points equal to your consitution (including enhancement bonuses and so on).

Incorporeal undead use vitality in much the same way as living physical beings, while corporeal undead have vitality representing the unnatural physical toughness of their mortal forms. In both cases wounds represent the strength of the creature's grip on the negative energy that sustains it, and is derived from Charisma rather than Constitution. Subject to this difference wounds and vitality work for undead in exactly the same way as for the living: undead are no longer immune to critical hits, and do not instantly depart when they reach 0 hit points (or wounds, in the new system).

Note that some Challenge Ratings may be changed to account for undead losing immunity to critical hits.

For the most part, vitality is interchangeable with hit points, with wound points comprising an additional pool to be removed when all vitality is lost. However, here is the crucial combat difference:

Rather than causing additional damage, a critical hit causes wound damage instead of vitality damage.

Weapons with a critical multiplier of 'x2' will retain their normal statistics (although the 'x2' is now irrelevant). For each +100% of damage beyond 'x2', the weapon's critical range increases by one. For example, most axes (20/x3) are now '19-20', a scythe (20/x4) is now '18-20' and so on. The Improved Critical feat and the keen magical effect now grant a one-point increase in the critical range: they do not grant +100% as before. Any other feature or effect that improves criticals by an additional multiplier of range or magnitude will similarly grant a one-point bonus, subject to a case-by-case GM tweak.

Spells that require attack rolls have a critical range of '20' by default. Other spells will continue to do vitality damage, although a critical failure on a save may invite wound damage.

Vitality recovers at a rate of one point per hit die, per hour of rest. I will probably award half that for an hour of light activity, but any hour that includes combat grants no respite. Wounds recover at one point per hit die per night of rest, or twice that for full days of rest (it is to this rate that the long-term care use of the heal skill applies).

The cure spells (and those like them) can now work in three ways: all vitality, wounds first, or half and half, to be chosen at the time of preparation unless you can cast spontaneously. Heal will work on a 'wounds first' basis, with excess points restored to vitality. The same principles apply to casting inflict spells to heal an undead creature.
When used to inflict damage, cure and inflict always affect vitality first.

A character with no vitality starts to lose wounds when injured (starting with the rest of the attack that took his last point of vitality, unless it had no excess damage). A character who takes any wound damage becomes Fatigued (cannot run, -2 Strength and Dexterity).

A character with no wounds remaining is unconscious, and will die at the end of ten rounds (count starting at the end of the current round). No more regular damage is counted; it's a ten-round timer unless somebody gets a coup de grace in before then. An appropriate heal check or any magical healing (even if it only restores vitality) will stabilise the character on 0 wounds, or the wounds restored by the magic, as appropriate. Note that this applies to undead characters (except that heal checks can't stabilise them), and if I can be bothered to do the book-keeping it may also be used for NPCs and creatures, if there is someone around who might be prepared to save them.
The death from massive damage rule is not in effect.

Abilities that allow incapacitated characters to fight on need reassessing, but I haven't yet done that.