A non-exhaustive set of RPG mechanics for turn-based online play.
The rules presuppose a social dynamic that includes the following and probably will not work correctly if these are not the case:
Here be dragons.
The basic roll is roll as many d6s as the stat, take highest, add bonus, evaluated as follows:
Where feasible and playing in person, let each player roll one of the dice: if not enough dice, work something out or the GM rolls them all; if too many dice, work something out or the GM rolls the extras.
If the highest results on both sides are equal, cancel them out one pair at a time until you have a winner or all rolls have been eliminated and the contest is truly tied.
If a roll wins, the winning character basically gets what they want: the lower the margin of victory, the more the GM may fudge the narration despite any controlling player's directions.
If the results are truly tied, neither side gets what they want.
If a roll loses, pick one of the following:
In any event, something must change so that no one can simply try the same thing again. The GM has full discretion over how diegetically long the result takes in order to effect this.
In doing all this the GM is directed to consider themselves a curator and compiler of the writings of the players and deference should be given to their narration even if none is given in the results. While storytelling skills are essential, under no circumstances should the GM be expected to serve as "the storyteller".
Each time a player gets a bonus of 3 (or whatever your standard maximum is) and loses a roll anyway, record it. That player now has a Butterfly that can be spent to alter a subsequent scene when it begins.
Upon spending a Butterfly, a player may add or change one element to the scene to their advantage, caused by that failure. Any causal chain, however convoluted, is acceptable, though the GM may interfere as needed to maintain background diegetic consistency. (Failing all else, or with the consent of the GM, Jungian synchronicity counts as causation.)
This change must not be so significant and relevant that it by itself basically resolves the underlying conflicts in the story.
Every affected character rolls a number of dice equal to their lowest stat, then adds the margin of victory/subtracts the absolute margin of defeat with no bonus. If the result is 10 or higher, that character avoids injury; otherwise, use the margin of failure to determine impact of resulting harm.
Injury should be capped at something proportional to the players' goals in initiating the fight: if they do not care if someone dies, then there is no limit.
Assuming no limit, life-altering things should probably start from a margin of defeat around 5-7, with anything over 10 leaving the character dead by the end of the scene.
Injury may be any lasting negative effect: destroyed or exhausted gear and supplies, or blocked escape routes, etc.
Each injury should do at least one of the following until taken away:
your bum leg gives out trying to climb to higher ground)
Thrakoz the Cruel's fire lance last round welded your bullets together. cannot reload)
you're smooth as butter until the barmaid suddenly narrows her eyes. 'Hey, aren't you that adventurer who...')
Non-combat: replace injury, if applicable, with other negative consequences which may or may not directly hinder the players' goals.
"GM-less" play: just before the roll, randomly or arbitrarily select one player to be the GM.
Not-really-opposed task checks: roll against static TN 5 or whatever the GM eyeballs out, unless the GM just says yes.
Strength, Charisma, Wisdom: do not go below 1; must add up to 7.
My sheet says she has a 'toolbox'.
How much history of the Martian Phoenix Dominion Order would she know? if it didn't occur to her to pack a #2 Robertson it's crowbar time...)
Write down 5 items.
Each "item" does not need to be a single discrete object. You can have, say, a brace of pistols and the ammo for it as a single entry - the important thing is that everything in one line item can all be comfortably carried at once and function for the same basic sort of task.
Diegetically of course you can have more stuff than this, but (unless you are deprived of them later) your access to these is more non-negotiable for advantage/disadvantage purposes. Otherwise, if it is at all reasonable for you to have had it on you without going out of your way to acquire it, roll Wisdom to see you have it with bonus/penalty or ad/disadvantage depending on contextual plausibility.
Any holes in backstory can be retconned as the game progresses.
Stats can be temporarily or permanently reduced by some injuries.
Every milestone, all PCs get 1 point to increase any 1 stat of the player's choice. What is a milestone? You should all know it when you see it.
Each PC should have 3 Virtues:
An actual diegetic town or city, even a building may have several towns for mechanics purposes.
Each must have at least 1 shop and 1 NPC connected to it, and a forum and inn.
A small clearing in the woods with a rock in it.
Get a big sheet. Map out the relationships between the NPCs based on the motivations outlined below. If this is visible to the players such that they obtain OOC information, the players should be trusted to play out dramatic ironies as appropriate.
NPCs may have some or all of the stats of PCs if the GM doesn't feel up to improvising on the spot later. A single NPC's combined stats should add up to 5, 7 or 12. An NPC's Virtues (if any) should be directed at PCs, an NPC or specific pre-established setting elements (which may be an abstract concept if the players have made it an issue during or shortly before play).
NPCs without Virtues defined should have 3 Drives: Kill, Fuck and Eat, directed at characters or setting elements as above. Make up particulars to establish exactly what each of these actually means.
Write down what the NPC will do that session if they are not stopped. It should be an attempt to fulfill one or more of their Drives, and its success or failure should change some relationships or infrastructure of the town.
Get a big sheet. Draw the rooms as the players encounter them. This should be visible to all.
If monsters continue pursuing the PCs out of the dungeon, keep doing more "dungeon" rooms as necessary representing areas in the path, forest, overcity, town, etc. beyond.
The GM may add a trap at any time, but until it is discovered every PC gets to roll at least once to detect it each time that PC comes into its presence.
Each room must have:
With respect to the areas, at absolute minimum you can have the middle of the room and near the walls and corners; on the other extreme your terrain areas may be 2 rooms in 2 buildings a mile apart in a sniper battle. It is not necessary that there be any way to traverse between all areas within a room.
The identity and nature of the action point and the means of triggering it need not be made explicit to the players.
If the players use an action point in combat, they gain 1 die, or in any event must roll at least 3 dice, in whatever roll is accompied with that use.
No GM-controlled character may gain a mechanical advantage through an action point until it is discovered by the players. If a player asks, out of character, if something is an action point, the GM is to answer honestly.