Boot Hill, TSR's third RPG (and second system, if we count Empire of the Petal Throne's system as a variant of D&D's) is very different from D&D. First off, it uses percentile dice almost exclusively. (One subsystem, for brawling, uses 2d6.) Second, it eschews D&D-style classes and levels completely - a character's capabilities are defined by their attributes, and by how many gunfights they have successfully survived.
This makes Boot Hill a major first: the first RPG without classes or levels. It's also another major first: the first RPG to be based in a historical setting, without any fantasy or science-fiction elements.
The character attributes in Boot Hill are:
Personal Accuracy (thrown weapons)
Personal Accuracy (fired weapons)
While these are set by rolls of percentile dice, these percentile values are not what is used in play (although they are recorded for use in the experience system). Each has a table that gives varying values. For example, for Personal Bravery, we have:
36-65 Above Average
81-90 Very Brave
Similarly, Speed and Personal Accuracy have 10 and 11 rankings, respectively, and Strength has 13, which are assigned numbers from 8 to 20, as well as descriptors.
Now, there's some argument over whether the original Boot Hill should be classed as an RPG. Some argue against it on the basis that the mechanics focus almost entirely on gunfighting, with no real rules for anything else. My perusal of the rules, however, makes me disagree with this - although gunfighting is covered by far in the most detail, there are rules for brawling, grappling, tracking, forming a posse, gambling, intoxication, campaign-level movement, hourly movement for long-distance chases, aging of characters, and sample prices and wages given.
To put it another way, Blume & Gygax seem to have made an effort to supply rules for what they considered to be the important parts of running a Western campaign and adventures. There's a lot of territory that they didn't cover - but there's also a lot of territory that original D&D didn't cover, and Boot Hill was working with a much shorter page count!
A second objection is that the original Boot Hill explicitly calls for players to play multiple characters, rather than each player playing one and only one character. However, Boot Hill does specify that each player should have a "personal figure" that is their primary character. This "personal figure" is given a boost in character generation, getting to add 10 to each die roll that is an 01-50, and 5 to each result of 51-70. Thus, looking at Personal Bravery above, we see that a personal figure is never a Coward. The actual results become:
26-60 Above Average
81-90 Very Brave
Thus, personal figures will have higher bravery than the average NPC 75% of the time, and will generally be Above Average or Brave (those two results being 55% of all results).
These personal figures are arguably the "player characters" of the players. This argument is boosted by the fact that early versions of D&D also tended to have the players each controlling multiple characters, via the concept of having "henchmen" and "hirelings". Indeed, it was quite common for one of a player's henchmen characters to become their new PC, if their PC died! Likewise, Tunnels & Trolls briefly mentions that individual players may have multiple characters as well, and such "character stables" were common with it, by what I've read from those who played it in the '70s and '80s.
As with many versions of D&D, Boot Hill assumes the use of miniatures. Ranges and movement rates are given in inches, as in early versions of D&D. These are fairly close to D&D movement rates, with people being able to "run and dodge" 12 inches or run 24 inches, and horses having a maximum "gallop" movement rate of 32 inches.
"Initiative" is called "first shot determination" in the rules, and is handled by calculating a total based on the character's Speed attribute, their Weapon Speed (six categories, from Very Slow to Very Fast, plus an additional one for "Already Aimed", which is regardless of weapon), Surprise Factor, their current Movement, how badly wounded they are, and modifiers for drawing two guns and/or hip shooting.
All these are totaled, and the character with the highest total shoots first, with shots then proceeding from highest to lowest. Wounds taken during the current round do affect order, so a character's ranking can drop before their turn comes up.
Note that there is no random factor in this determination: initiative order is deterministic, although one's ranking can vary according to what you are doing in the current combat turn. The best possible result is 35, for someone with "Greased Lightning" speed who has already aimed. (Hypothetically, it could be 38, but it seems reasonable to assume that "hip shooting" does not matter when one has "already aimed". Remember, early RPGs tend to assume that players and GMs will interpret the rules according to logic and common sense, and not blindly follow them.) Conversely, the lowest possible value is -70, for a Slow individual drawing two Very Slow weapons, who is running, completely surprised, and has taken wounds lowering their current Strength below 1/2 of maximum.
When a character gets to shoot, their chance to hit is calculated. The base chance is 50%, with modifiers for Range, Firer Movement, Target Movement, Individual Accuracy, Wounds, Personal Bravery, and Personal Experience. There is also a table of miscellaneous modifiers, for such things as shooting from the hip, concealment, resting your weapon on a solid object to steady it, and so on.
Personal Experience, in the form of how many gunfights the character has survived, makes a very large difference. A character who has not been in a gunfight before is at -10, and parity (in the form of a 0 modifier) is achieved after surviving three gunfights. At maximum, those who have survived eleven or more get a +20 modifier, boosting them to a base hit chance of 70% - almost double the 40% of someone who has never been in a gunfight!
It's possible to have a greater than 100% chance to hit. This gives nothing special, beyond the fact that this will help greatly if trying to fire multiple shots, since each additional shot gives a -10 to all the shots fired!
When a shot hits, the hit location is determined. This is either by the "fast method", which takes one roll, and simply determines whether the hit is a "light wound" (-3 to Strength), "serious wound" (-7 to Strength), or "mortal wound" (instant kill). The "exact hit location chart" requires two rolls: the first determines the hit location, and the second determines the damage done, based on that location. Damage amounts are the same as in the "fast method", but the chances vary by location. Thus, leg, arm, and hand wounds are never mortal, but shots to the head have a 60% chance of killing.
When using exact locations, hits have other effects as well - for example, a light wound to an arm gives -25 to speed and accuracy with that arm, while a serious wound prevents use of that arm for shooting at all.
Cover is handled through the hit location system - if the area hit is behind solid cover, no damage is taken. Concealment of more than half the body gives a -10 to the chance to hit.
Brawls are handled through a separate Brawling Chart, which consists of a Punching Table and Grappling Table. Initiative is decided by the characters' unmodified Speed attributes, or by surprise. The opponent with initiative may make two punches; the slower opponent may do so if they have an advantage over the foe (gained from results in previous rounds of brawling).
Either one can try to grapple, but if they do, that is their only action for the round. Similarly, knives, clubs, chairs, gun butts, and other weapons allow only one attack in brawling.
2d6 are rolled for each attack, either on the punching table or the grappling table, as appropriate. The result indicates how much (if any) Strength the target loses. Punches are affected by whether the right or left hand is being used. The rules don't actually specify how to determine this, but presumably when two punches are allowed, it's one from each fist, and a seriously wounded arm can't be used to punch, just as it can't be used to shoot.
Results can also include modifiers to your opponent's next attack, and/or to yours. The grappling table has a few 'special' results - if a held opponent manages to gouge your eyes or knee you, they break the hold instead, and an armlock on an opponent gives them a -1 to punch attempts with that arm and to all grappling attempts. If an opponent chooses to pull a gun and shoot, any minus they have from punching and grappling is multiplied by 10 and applied to their chance to hit with the gun.
When grappling, once a lock is established, the attacker can continue it automatically each round, until the held party breaks free. Breaking a hold is done on the grappling chart. Exactly how this works isn't described, leaving it open to some amount of interpretation.
In any case, though, an opponent reduced to zero Strength by brawling is only knocked out, and will wake up 5 minutes of in-game time later. Bludgeoning weapons subtract 1 or 2 from the attack roll, but add the same amount to damage; knives are treated like punching, but if a hit is made, the rules for gun damage are used instead.
The advanced rules allow some interleaving of movement and combat (in the basic rules, all movement happens before shooting, so someone running from cover to cover cannot be shot at unless it's too far to move in one combat turn). It also allows Indians (and only Indians, by a strict reading!) who are using bows to arc their arrows over cover under some circumstances. Morale rules are added for minor characters (which includes those controlled by player who are not their "personal figure").
Optional rules add a determination of how many shots a character can fire before another character gets to start shooting. In the basic game, someone whose weapon has a rate of fire of 3, for example, gets to fire all three shots before the next character fires any, even if their calculated First Shot Rating only differs by one point. Further options allow characters to be stunned by attacks, be intoxicated, add a "gambling rating" for gambling contests, and rules for the use of dynamite, misfires (which is handled as a separate roll each time a gun is fired), stray bullets (allowing misses to hit someone else in the line of fire), gatling guns, and cannons.
The Campaign rules have turns that last a month or a week. When a turn results in characters meeting up in a potentially hostile situation, chases and tracking can then be played out, possibly resulting in fights. Aging is added as well. Characters starting age is determined with 5d10 (so they could be as young as 5!). Those under 25 improve with age; those over 35 lose points with age.
Experience also matters in campaigns. In addition to the built-in improvements in accuracy for surviving gunfights, each successful showdown allows the winner to add to Speed (+2 if under 51, +1 if under 81), Bravery (+2 if under 66, +1 if under 91), and Accuracy (+3 if under 26, +2 if under 51, and +1 if under 86). A note is made that these should be multiplied based on odds - that is, if one character defeated two, they improve twice as much, or only half as much if the winners were the side with two people, and so on.
To get a feel for the system, my friend Julian and I made up a couple of characters and played out two gunfights - one a short-range pistol duel, and the other a longer-range fight with rifles. We then played out two brawls, one with only our personal weapons available (i.e., knives), and the other a bar-room brawl with chairs, bottles, and so forth.
We got a few observations from this:
First off, combat is deadly and random. Even though one character had a clear advantage in stats, that didn't seem to matter much. Your "hit points" are merely your character's Strength, varying from 8 to 20... but that doesn't make a huge difference when 15% or 22% (depending on whether you're using the "fast hit location method" or the "exact hit location chart") of hits are instant kills. Two "serious wounds" will kill an average person; two and a light wound will kill 90% of PCs.
(Side rant: one would think that game designers would make sure that alternative systems that are supposed to be equivalent have equivalent results, especially when the math isn't very hard. However, in this case, the "fast" method gives a hit breakdown of 50% light wounds, 35% serious, and 15% mortal, while the "exact" method gives 35.25% light, 42.75% serious, and 22% mortal, making it considerably more deadly. This is compounded by the fact that the exact system also gives penalties based on wound locations. For example, a light wound to a leg halves maximum movement, and one to your gun arm gives -25 to speed and accuracy. Thus, if anything, if would make more sense for the exact method to be less lethal, since it adds in penalties for being wounded!)
Even without guns, combat feels very random: your character's statistics literally make no difference whatsoever in the brawling rules, except for Strength determining how much damage one can take before going unconscious. On the bright side, the results given by the tables are all given names, such as "glancing blow", "jab", "head lock", etc., making it easy for a GM to colorfully describe a fight (or even for colorful fights without a GM!). However, since it's basically a random dice-rolling exercise with almost no strategy or tactics, it can be quite frustrating as a player. And if someone pulls a knife, combat turns very deadly!
Something else we noticed, in looking over the sample scenario and through early articles in The Strategic Review and Dragon for Boot Hill (notably, the writeups of Western heroes and characters from Western movies and TV shows) is that your characters, while likely to be slightly above average, are by no means 'heroes'. The writeups of those heroes almost universally have far above-average stats. For example, Wyatt Earp in the sample scenario is given Speed 97, Gun Accuracy 96, Bravery 97, and Strength 99, plus 9 gunfights worth of experience. Only one listed character in that scenario has an average of less than 70 in their stats, and most are better than that: the average stat across the 11 characters given in the sample is 82!
A quick check with anydice.com shows that about 2% of characters will have an average of 80 or better, taking only the four stats given for the scenario characters. To add insult to injury, since the experience system caps the abilities it does improve (at 81, 91, and 86), and never improves Strength, it's not even possible for a character to work their way up to the level of the 'legendary heroes'. You either luck into being that good, or never get it at all.
Even then, advancing requires surviving a lot of gunfights (brawls don't count, by the rules as written)... which, given the lethality of the rules, isn't too likely. Since one cannot increase Strength (and thus hit points), and there is no defense skill or attribute to improve, lethality to all characters is likely to simply increase over time as everyone gets more accurate.
Boot Hill is an interesting departure, and presages many things that other games would do later: percentile-based mechanics, hit locations, wound penalties, and a classless system all make their first appearances here. Unfortunately, the Western genre was already well past the peak of its popularity, and the realism of the system likely did not appeal. With it very unlikely that one would get a 'heroic' character, no reasonable way to advance characters to such levels of skill, and low survivability, it was poorly suited for long-term roleplaying by people who became heavily invested in characters. With quick character generation and fast mechanics, it could have been well-suited to one-shot games, but genre limited its appeal.