Apercu here gave me some good advice about just getting my ideas out there. So I'm going to use this thread for just that. I'll try to make sure each idea I come up with will have a few paragraphs devoted to it. Mostly they'll be be fighter/warrior type boosts, general house rules and character/setting ideas, to be fleshed out in other threads. Here it goes.
Disabling Attacks
You've seen it in movies and TV shows. A crazed and or ruthless shooter attacks, but the heroes can't get a good shot at center mass without hitting friendlies or innocent bystanders, but they can get a shot in at the knife or gun hand. So they take it, saving the would be victim and leaving homicidal screw-up with one less fully functioning limb to kill or maim with. So I'm going to attempt to import this to D&D, LL, Mutant Future and similar games. Here it is.
Battle is often brutal and harsh, with the death of one party, or more parties, a likely outcome. But particular individuals of heroic ability (read as PC grade) can make targeted attacks meant to disable, not kill their foe. When describing the targeting of a specific limb while making an attack stunt the combatant may deal damage to that extremity instead of the main body of his or her enemy. This deals the same amount of damage as a normal attack would, with a number of hit point equal to the creature's maximum hit points. Loss of limb function occurs at zero.
Reducing a pair of limbs to half maximum hit points hampers them, with either a disadvantage or a -2 to all rolls requiring one of those appendages, possibly disarming them or costing the enemy its shield bonus. If you hamper a pair of legs that creature loses its movement speed. If you damage a pair of limbs to -Con one of those limbs is either severed or otherwise so damaged that only powerful restorative abilities will mend it, like regeneration. As a side note, the head is counted as part of the normal hit point pool, along with the torso, so no trying to get an instant death headshot. You know who you are! In addition, the legs count for half of the core hit point total, if targeted. This could also be used for ripping monsters limb from limb Beowulf or God of War-style.
Note: Damaging a creatures limbs isn't necessary to kill or generally incapacitate it. Also damage to arms has no effect on core hit points.
Note: Against significantly larger creatures, such as dragons and giants, melee attacks by medium or smaller assailants against the creature's core hit points, in other words their actual hit points, are impossible at floor level with the gigantic creature. This requires one of two things, climbing or flight to reach the monster at chest height, or attacking the legs to bring it down.
Note: Attacking a creature's legs alone won't kill or incapacitate it. The finishing strike must be against the head/torso region.