Alien has armor that is rolled to reduce successes to hit; extra to hit successes increase damage. Parries/dodges likewise can reduce successes.
Twilight 2000 2, & 4 both have reduction by armor on location.
FFG Star Wars uses brawn+ worn armor to reduce fixed+ to-hit successes damage. Some armors also add penalty dice on the to hit.
Talisman Adventures uses staging damage reduction. When you take a hit, the armor loses a point of effectiveness for the rest of combat; a short rest restores all but 1 of those. The lasting damage can be repaired as well, but takes material to do so.
Given most weapons are 1d6, with some being 1d3 or 2d6, and add Strength (which for PCs is 2-7 range), and armors run to mid-teens for heavy stuff... the Fighter's 15 points of worn armor are really potent... but he has to pick the baddest target in order to protect others from same... And his closest call to death was 8 bats, not a single nastybad foe.
Traveller has armor soak. Works great, but the game also has flat progression which likely makes it easier to design.
Only in certain editions.
- CT: armor is a table of to hit mods by weapon.
- MT: Armor reduces damage by a comparison of pen to AV, and is a multiplier (×0, ×0.1, ×0.5, or ×1, by specific comparison). Note that margin of success also multiplies (×0.5, ×1, ×2, ×4, or ×8), rounding is after cumulation of both factors to fixed base damage. (After combat, damage points taken convert to dice of attribute loss.
- TTNE: Armor is by location damage reduction
- T4: armor converts it's rating in dice to 1 pip each
- T5: don't recall; too lazy to look it up.
- T20: Armor reduces lifeblood damage, but not Stamina loss. And not by simple subtraction. Each AV either removes a die from the count for LB losses, or, if only one left, is a -1 on the die. Armor has no
- MGT (both) armor reduces damage, but margin of success increases damage. Armor is a subtraction.
- GT (and all GURPS, in fact) is dual factored: DR is direct reduction, but there's also Passive Defense (PD), which is rolled against to entirely cancel a hit.
I own Pendragon but despite admiring a lot of things in the system I've never actually played it and really doubt I ever will.
As far as the armor thing goes, it shares a lot of its system with Call of Cthulhu, and it deals with it by more or less building armor into its game expectations in the sense that it's a game of knights so pretty much everyone should be wearing armor and all the armor everyone wears (or is likely to be wearing) is very similar. It can therefore build what balance it actually cares about, and I'm not sure Pendragon cares much about balance at all. It would be very hard to adapt a game where average damage is like 5d6 and a small dragon does 16d6 x2 damage to OSR.
It is a variant of BRP, more specifically RuneQuest rather than CoC.
Damage scales differently in Pendragon, tho.
Noting that typical pendragon damage is 4d6, and typical armor is 10 to 15...
most BRP games, damage is 1-2, rarely 3, dice, number of sides by weapon, and armor values are single digit.