In almost every instance, I forgot what ruleset we were using at some point. Which is a good thing. Once chargen is over, you spend a lot more time describing your characters actions and poring over the GM’s descriptions than you spend interacting with rules. When you do roll, it’s usually a combat to-hit roll, which you’ve probably programmed into the online dice-roller as a macro. Pretty much any game will work for PbP.
But that doesn’t mean there aren’t points of possible optimization.
Point 1: Resolution. Anything that can keep the action moving is a boon to PbP. A game that requires a back-and-forth exchange of information to resolve an action is going to progress very slowly. A good rule of thumb is that it’ll take 2 or 3 days to get a response from any given player. At that pace, an exchange that would take seconds at the table can become a week or more on the boards.
Point 2: Facility. It is not easy to learn a new game (one that operates in a fundamentally different way) over PbP. The drawn-out nature of communication spreads out the points of engagement with the novel system too much. It’s like trying to learn tennis when you only get one swing of the racquet a week. And each time you have to ask a clarification question, you’ve bogged the game down again.
Point 3: Accessibility. You can’t pass a copy of the rulebook around the table when you’re playing PbP. And not everyone is going to want to plonk down cash for a game they haven’t played. So it’s helpful when there are legal ways to digitally share the rules with the players.
A good PbP ruleset, then, would be optimized in the following ways:
1. As much as possible can be resolved in a single turn. It could be one roll or multiple rolls, but you can do them all in one go without having to compare or respond to other rolls, or having to negotiate the interpretation of the results.
2. Anyone who has to resolve anything via game mechanics understands them well enough to apply them without prompting.
3. Having the at least the player-facing rules available either online or as a pdf.
So, let’s examine some rulesets.
Resolution: This is the baseline from which we hope to improve. Many actions require rolls from both player and GM. Hopefully a player knows to roll damage at the same time they roll to-hit, or else that doubles the length of the exchange.
Facility: Hard to be much more familiar than D&D.
Accessibility: Most retroclones have free versions, and most people interested in OSR games will have copies of at least a few editions around.
This is the ruleset I’m currently using for my GARGANTUA game.
Resolution: You’re never more than one die roll away from knowing how things went. Combat is just a straight damage roll. When fighting breaks out, everyone says what they’re going to do, and appends a damage roll to their post. I collect all the rolls, and reveal the rolls of the monsters, and stitch a narrative together to explain them. It’s very fast, very deadly, and we’re off to the next round.
Facility: A little tricky. ItO is so pared down that it takes some real thought when and how to apply some of its mechanics. And it’s so minimal that I’m making up mini-game mechanics on a fairly regular basis. Which is good fun, but not facile for the players.
Accessibility: There’s a free player-facing pdf.
Resolution: The irreducible minimum of rpg mechanics. Say what you’re going to do and roll a d20, and let the GM interpret the results. That’s pretty straight forward. However, this strikes me as such a simple system that either the players have to be on board for arbitrary rulings, or the GM will have to build their own rubrics or something to ensure any degree of consistency. And, sadly, you’d have to jettison the magic system, which is performative (the player has to recite a few lines and act out a hand gesture, and the GM penalizes you for any stumbles).
Facility: Couldn’t be easier. Player’s simply add a d20 roll whenever an outcome is in any doubt.
Accessibility: Freely available, and easily summarized in about three words.
Resolution: Whitehack involves a lot of negotiation between the GM and the players to resolve actions, determine the cost and effect of magic, and to build the world as you play. Players would very rarely be able to determine the mechanical effects of their actions independently.
Facility: Whitehack’s classes are beautifully abstracted in a way that really opens up the creative possibilities of chargen. But it also takes a bit of work to wrap your head around. Chargen being mostly a one-time affair, this isn’t too much a problem. But Whitehack also uses contested rolls, including a blackjack-style bidding contested roll that must be tremendous fun in person, but would be a grinding eternity in PbP.
Accessibility: Whitehack is only available as a physical book.
Whitehack is a brilliant game, and you should check it out, but it is very much not optimized for PbP. It's on this list to provide contrast.
Resolution: All the rolls are put in the player’s hands. You roll to hit in combat, and you roll to not get hit. Most other rolls are simple roll-under stat checks, which are very easy for a player to roll proactively based on their description.
Facility: The Black Hack incorporates a number of houserules that have been floating around for a few years, but some of them may be novel to your players. But they’re very consistent. If the GM made a concerted effort to establish the combat mechanics and usage dice early on, TBH should allow proactive mechanical resolution from the players.
Accessibility: There is an SRD available, and TBH is open game content, so you don’t have to feel bad copy-pasting into your forum’s rules thread.
Resolution: Like its inspiration, Into the Odd, Maze Rats puts all the mechanics in the players hands and keep resolutions one-roll simple. But a big part of the game is negotiating with the GM to try to avoid having to make a stat check, because you are likely to fail. I think this could work very well once the players understand that their job was to describe their actions so plausibly that it didn’t trigger a roll, and then the GM made the roll in reaction to insufficient description.
Facility: Maze Rats uses a 2d6 mechanic that is consistent and very easily digested.
Accessibility: The pdf is pay-what-you-will, and the mechanics are so simple that you could summarize them in a couple sentences.
Thank to the encyclopedic +Sophia Brandt for bringing this ruleset to my attention. It specifically designed for PbP.
Resolution: Spaces streamlines play by giving all the rolls to the GM. This could be controversial. Most players that I have encountered really want to be the one to trigger the randomization of their outcomes. There’s a powerful connection to that split second of uncertainty after you roll the dice (or click on a “roll the dice” button) that is hard to give up. That said, I’m in a B/X game right now where the GM is making all the rolls, and I’m really enjoying it. I find myself investing more effort in describing my character’s actions to guide the GM’s evaluation, rather than just hitting my melee attack macro. Which is exactly the effect that +Brent Newhall predicts for his ruleset.
Facility: In this case, facility refers less to the player’s ability to absorb the rules than to the GM’s ability to keep track of all the variables. I haven’t played Spaces, yet, but it looks to me like it is simple enough to track. Character’s look an awful like OD&D one-line monster stats, and pretty much everything is 1d20+Level vs. a target (opponent’s AC for combat; your AC for physical stunts; 15 for saving throws). Level is the only variable to track, and the party levels up together, so that boils down to one macro. Nice.
Accessibility: Free cheat sheets are available.
The Black Hack relies on a spell list derived from the old school classics, and asks for a single stat check to see how it goes. I expect that this would work pretty well. Old school automatic-success-but-saving-throw spells work well, too.
Maze Rats and Whitehack both require negotiation on a spell-by-spell basis, which is not optimal.
Looking over this, it strikes me that there are two broad categories:
1. Basically D&D games that are workable but not optimized for PbP
2. Really minimal games that are pretty optimized, but maybe too spare, especially in character choice.
The system that seems to inhabit the space between them is The Black Hack. Its mechanics tend to be pretty optimized, but you can play a Conjurer with a full spell list (to say nothing of the one million home-brew classes floating around out there).
I think a good future project would be to write a version of the Black Hack specifically tailored to PbP. Maybe call it The Post Hack.