Octas, is a tabletop role-playing game system (yes, another one!) which, in its base form, is intended to have the following characteristics:

All of the above decisions are based on my own personal game-play preferences and should not be taken as an assertion of any kind of superiority. For example, there is nothing wrong with combat-focused mechanics, it just isn't how I like to play this type of game at this stage in my life.

Decimal counting is definitely awful, however, compared to just about every other reasonable alternative!

A Shared Story

Chances are, you are familiar with the concept of a Role Playing Game. If you are new to this concept, then Octas may not be the game for you, primarily because it uses dice and the numbers they produce in a way you are probably not accustomed to, and that extra level of learning is likely to overwhelm your learning of general Role-Playing Game concepts. If you are new to Role-Playing Games, then I recommend cutting your teeth on a more conventional Role-Playing Game system, particularly any D100 skills-based system if you want something similar to Octas in spirit, but friendlier.

In brief, a Table-Top Role-Playing Game (TTRPG, for short) is a game played by a group of people. It is largely about cooperatively telling a story. It is traditionally played around a table (hence the name) but today remote-play via computer network is also a popular alternative, and provides access to a much larger pool of players.

In the game, one person acts as the controller of the game (generically called the Game Master, or GM for short) this person supplies the framework of the story - such as the surrounding world, key events and supporting characters.

The other players (commonly called Players, go figure!) each play the part of a major character in the story. Within certain limits, defined by the game's rules, they dictate how their character reacts to both the story framework provided by the Game Master, and to other players' characters also operating withing that framework.

A random element, in the form of dice rolls, is also used to provide some added mystery and excitement to the story by introducing an element of unpredictability.

A player is, of course, not their character. Characters have their own sets of attributes and skills that frame their interaction with the story, under the players' guidance. A player may be smart but socially-shy, but their character the opposite. A combination of the players' role-playing and some relatively simple maths linking character attributes to dice-rolls aids in separating the two.

In the process of creating the story, the Game Master is regularly in control of agents acting against the player characters. This, however, does not mean the Game Master them-self is working against the players. The aim of a TTRPG is not to beat the Game Master, or the other players, but to be involved in the telling of a good story. Good stories have antagonists and setbacks for the main characters to overcome and the Game Master's actions in providing these is in the service of making the story the best one that they and the players can make together. A side effect is that the Game Master has a vastly dis-proportionate amount of power in the story, but a good Game Master will wield that power in the service of keeping the story going, for the players and for themselves.

It is largely a matter of balance - make things too hard on the players and they will become frustrated. Make things too easy and they will become bored. The exact sweet-spot will vary between player groups and even with the same group at different times, so it isn't something you can write hard rules on, but must be left to the Game Master's judgement at the time. Game Mastering (well) is a lot harder than playing (well or badly) - I generally prefer being a Player, myself, but GMing has its own rewards for all that extra work too.


There are different play-styles for TTRPGs, even within a single rule set, so be aware that different groups of players may have quite different expectations of how a game should be run. The two extremes are:

Mechanics-focused: this style of gameplay gets deeply into the mechanics of combat statistics (essentially relatively simple, but extensive, maths) and living - and dying - by the results of the dice. There tends to be a fairly strong focus on materiality in these games with the killing of monsters for points and the collection of treasures for the sake of having lots of (imaginary) wealth.

Role-play-focused: At this end of the spectrum, players are all about the story. Combat and dice rolls are largely for flavor and variety, and it is all about making an interesting and exciting story together.

In reality, most players and games are somewhere in between these two extremes, and will even wander up and down the spectrum a little over the course of a single game. While I, as do most new TTRPG players, began very much at the mechanics-focused end of the spectrum, these day I am planted well on the role-play side, and Octas un-apologetically favours this play style.

If starting a new game group, it is a good idea to have a bit of a chat about expected play styles. Inexperienced players probably won't know their own preferred style, and this is fine: a whole group of inexperienced players will naturally find one over time.

If joining an existing game group, it is a good idea to check with the GM what the group's play-style is. You don't have to exactly match it, but if you are too far off, you may find less enjoyment in the experience. This is not due to any fault any more than someone who hates ice-cream at an ice-cream party should fault the ice-cream party... or even themselves! They just need to find a cheesecake party. Mmmmmm!

Pieces of 8!

Octas, as the name may suggest, was designed to natively use a numeric base of 8. Why base 8? Why not. Frankly, if I was going to use a numeric base of 10 or (effectively) base-20, or a weird mixed-base system of numerous platonic-solid-shaped dice, I would use one of the many excellent existing TTRPG systems out there that already do that. I happen to like a numeric base of 8: It is mathematically 'cleaner' than base-10, and also easier to use (assuming you don't have a lifetime of legacy base-10 stuffing up your head, as we all unfortunately do). Also, the way the dice worked out physically, from the part-truncated-octahedral shape, to the hexagonal dot arrangement of the number indicators, turned out to have an unexpectedly satisfying aesthetic.

I actually made the dice set first, as a 3D-design-and-printing self-training project, I deliberately made dice that had no actual use, because why go to all that trouble to design and manufacture something I can already buy ready-made for far cheaper! Then people kept asking me what game they were for, and I got sick of answering 'none' so I began Octas!

Having said that, the rules work perfectly fine in Decimal and there is an appendix which provides instructions for alternative base-10 play using a pair of 10-sided dice, you barbarians!

Barbarians!: The ancient Romans, who were big fans of decimal, used the word barbarian to mean "anyone not of the Roman Empire" with a contextual implication of those persons being less civilised, though not necessarily primitive in any other way. My using the modern version of the word to jestingly describe all of us users-by-default of decimal is a deliberate irony. (See the Appendix All Your Base for more of my incoherent ramblings on this topic).

Dozenalists could likely also adapt the rules to 12-sided dice (numbered 0-↋) with little effort, too.

Whatever numeric base you use, use it exclusively: don't mix bases or things will break! So pure octal or decimal (or dozenal!) it has to be. Pick one!

Still, the game is called Octas, so the number 8 is going to feature quite a bit, even when playing in other numeric bases, just not where it will have much effect on the ease of game-play.

Also, it is largely only the dice that work in octal, and the game itself is still presented 'translated' to decimal with a bit of simple maths to convert between the two systems.

Die Die Die!

In line with its octal numeric base, Octas, uses 8-sided dice (or die, if you prefer the archaic version of the word), the official form being a regular octahedron with the 'top' and 'bottom' points rounded for the benefit of bare feet everywhere! Numbering is 0 (a blank face) to 7. Convention is to use dots arranged in a hexagonal pattern rather than culture-specific digit-symbols. The hexagonal arrangement was chosen as it provides visual cues that allow surpassing the normal human subitizing (sight-counting) limit, which other spatial arrangements were found to be problematic with at this number of dots.

Dimensionally, the official dice are about 21mm on each side-edge and the smoothing of the top and bottom points brings the height down to 21mm as well. These dimensions are the 'standard' but are in no way required and you should feel free to use whatever you have at hand.

8-sided dice from different sides, showing all faces

You can also use regular Hindu-Arabic-numbered octahedral gaming dice and treat the symbol '8' as the zero.

One of the two dice has an extra mark on the top and bottom (rounded) points to avoid confusion/arguments as to which is the most significant (first-placed) digit in rolls in which the dice are to be read as a two digit octal number:

Two 8-sided dice with precedence marker on left one

Note: Although the Dice are octal, all the numbers used in this set of rules are in decimal. The base-conversion is built-in to the rules.

If you are the kind of person (masochist?) who would actually want to play octas in actual octal (as The Ancestors intended), you are already quite capable of back-converting the decimal numbers listed in these rules: Almost all of the numbers over 7 are nice round ones (in octal), so even doing it by rote-memory is just your 8-times tables in reverse. See also the appendix Playing Octas in (Actual) Octal for more details on this.

And here is a free STL of the dice pair above for anyone who wants to 3D-Print their own. Enjoy!

Octas has five possible ways in which the dice can be used, each with different skew to the results probability:

Unit Die, abbreviated '1D': one dice is rolled. The result is a number 0-7. All results are equally probable.

Unit Die High, abbreviated '+D': both dice are rolled. The highest of the two results is used, the other discarded. Probability is significantly skewed towards higher results.

Additive Die, abbreviated '2D': both dice are rolled and added for a result 0-14. Middle-results are somewhat more probable than results at the extreme ends of the range.

3D, 4D, etc. likewise would mean 3 dice added, 4 dice added, etc. However, since the standard Octas dice set contains only two dice, the normal rules do not have more than two dice in play at any time.

Additionally (heh) static numbers can be specified to add to a dice roll. The shorthand for this is D+X where D is the dice roll, and X is the number:

Shorthand Meaning Results Range
1D+2 Roll 1 dice and add 2 2 to 9
2D+4 Roll 2 dice, add them, and also add 4 4 to 18
+D+1 Roll 2 dice, take the higher result, add 1 to it 1 to 8
1D-8 Roll 1 dice and subtract 8 -8 to -1

Tip: for 1D-8 rolls, specifically, it is easier to just treat 0 as 8 and put a - (negative) in front of the result. The probability of any result will be the same. This only works for 1D-8 rolls and not for other rolls such as +D-8 where doing this would reverse the probability skew from what is intended, so for such rolls, the maths will need to be done!

Double Die, abbreviated 'DD': both dice are rolled. The dice with the precedence mark is the upper digit, the dice without it, the lower digit. Results range from 00 to 77, in octal, which is 00 to 63 after conversion to decimal. All results are equally probable.

Unlike most 'D100' dual-10-sided-dice systems, Octas does not treat a roll of 00 as 100, so the maximum roll is 7-7 (63 decimal after conversion), and minimum 0-0, for zero. For this reason, the Octas dice system can also be referred to as a D77 system (if you did it with decimal dice, you might call it a D99 system... and using dozenal dice, a D↋↋ system, presumably).

Double Die High, abbreviated '+DD': both dice are rolled. The dice with the higher result is the upper digit, the dice with the lower result the lower digit. Results are again 00-77, however result probability skews significantly high.

Technically you could also flip both the 'high' ones for Unit/Double Die Low, but no justifiable use has yet been found for these variations, so they have - for now at least - been left out to avoid unnecessary confusion.

Base Conversion.

When rolling DD or +DD dice, you must convert the results to decimal. For this you will need to know your 8-times-tables (though only up to 7x8) and also know how to add two-digit numbers!

Multiply the high dice result by 8. Then add the low dice result to that.

So a DD roll of 4-3 is (4x8)+3 = 32+3 = 35 in decimal.

Yep. That's it! ... To be fair, converting from decimal to octal is a bit more involved, so the game mechanics avoid needing to do that!


Octas is intended to be genre-neutral.

Included with the base Octas rules, is a genre expansion for the fantasy-wrapped hard(ish) sci-fi world of Octas (no italics) as an example setting for the Octas rule set. This should be considered entirely optional, but I do hope you like it!

Other genres, from mystic to Kafkaesque should be entirely possible, so feel free to knock-yourself out satisfying your own story-telling itch!

While the general rules are written with the world of Octas in mind, it is deliberately very lightly linked in, so replacing it should be trivial, requiring no more than swapping out a few world-specific names for things. For example, the magical system of Octas ties into the Daemonic language, and this whole language would be removed for a game that is set in a world without magic, or re-cast into something genre-appropriate.

The spelling of the Dæmonic language skill on the character sheet is a deliberate separation of this aspect of the rules from the fantasy-world concepts of 'Demons'. In a modern context, for example, a Daemon is a kind of 'helper program' in a computer operating system (not by coincidence: these programs were originally named after a class of small helpful Daemonic entity of folklore), so in a modern or futuristic setting without magic, a skill with the Daemonic language might be validly re-interpreted as a skill with computer interfacing, either via programming or a knack for effective structured-database-query wording. Or simply having the right voice-tone and phraseology to consistently not be mis-understood by speech-recognition systems!

Roleplay focus

As mentioned above, these days I am primarily focused on role-play rather than combat mechanics and the Octas system skews heavily that way by intention. While some risk is necessary for this type of game, the mechanics are deliberately focused away from character-termination. As a general rule-of-thumb, a character should not be able to die from bad luck alone. Bad player judgement (including bad probability-assessment) definitely carries the potential for character death, however.

Generally, a player should, with enough thought and effort, be able to role-play their character through any situation the Game Master can throw at them, with the dice roles being more about the flavor and details of the events. Of course, if in full knowledge, they still choose to take big risks, then the rewards or losses are theirs to bare. That is part of the fun, but it should ultimately be the player's choice how much risk to take on, though tempting them with the prospect of greater rewards is definitely part of the Game Master's role.

Where next?

The next stop would be the volume Creating a Character. This will, as the name suggests, cover the creation of a character for use in the game. After that, the volume Having an Adventure will provide a general guide on using your characters to create a story, along with some tips for getting the most out of the story-telling aspects of the game.

People wishing to take the role of Game Master should also read the Creating a Character and Having and Adventure volumes first as they provide important context for how player characters work and what players will expect from you as their GM, as well as the bulk of the rules for general game-play.

GMs should then look at the Game Master Guide which contains all the additional rules that normally only the GM needs to deal with, as well as tips specific to optimising the game experience from the GM's perspective.

Players do not need to read the Game Master Guide, however there is nothing at all secret about its contents, and looking certainly won't hurt. More experienced players may find a knowledge of the rules from a Game Master perspective can even help them in working with the Game Master to improve the story told. Just be wary of meta-gaming, where the players start using their knowledge of the rules to circumvent the story-telling spirit of the game, often without even realising they are doing it. See also rules-lawyering on a TTRPG wiki near you! Your play-group may also like to rotate the role of GM from adventure to adventure, so sooner or later everyone will get an in-depth knowledge of what is in the GM manual anyway.

There is also an Extended Rules volume which provides additional rules that more advanced playing groups may like to incorporate into their games, but which beginning groups will likely find a bit onerous while learning the basics of the Octas game system.

Octas tends to assume all its own rules are advisory rather than strict, but to what extent this is applied is up to the individual player-group: you can play it both ways, and any in-between, as long as the whole group agrees. Ideally, in advance! Just be wary of arbitrarily changing rules for ill-considered reasons, as the rules-laid-out have had some thought put into them concerning trying to keep the game reasonably balanced to play.

DevNote: Once we have actually done some play-testing we will add mention of this here too!

There are also a number of companion volumes that are specific to the provided default Octas/fantasy world. They are the files located in the octas-fantasy section. These may be used as is, or used for ideas for creating similar volumes for different worlds or genres. These will be referenced from the rules manuals as appropriate, so you need not explicitly read through them until you are directed to them, and if you are substituting a different world or genre, those replacement documents should be written to seamlessly replace the supplied ones for the Octas world.

So if you are playing a SciFi genre, for example, wherever the manuals refer you to an Octas/fantasy manual, you should look up the Octas/scifi manual of the equivalent name. And the writer of said Octas/scifi manual should try to cover the equivalent content in as close-to-compatible format as possible, to make genre-hopping as painless as possible for their players.

Beginning players may want to not read certain parts of the Menagerie, in particular. Though the narrative-focus of the Octas game system means that a curious poke through this volume shouldn't really have any effect on game-play itself, it does represent significant 'spoilers', and you may want to skip over it in favour of learning about the creatures and places of the Octas world while playing the game. Once you have become familiar with playing Octas as a default human character, however, the first section of the Menagerie, dealing with Sapient Species, contains information that is needed by players if they wish to play non-human characters in the Octas world.

Also the 'Behind the Curtain' appendix is a big no-no if you don't like spoilers, as that is where all the sci-fi under the fantasy is explained, mainly to assist GMs with creating their own world-consistent content, and even GMs can safely ignore this information until they are ready to leave the safety of the supplied content, and start creating their own new things for the Octas world. After playing for a while, you may find this section interesting, but for best game-play enjoyment, it is recommended you go in blind regarding this aspect of Octas: nothing about the behind-the-scenes will provide any in-game advantage for players, so reading it won't actually ruin the game-play... but it may dampen a bit of the initial wonder you experience in this new world.

As a personal note, I do rather hope most people do eventually read the Behind the Curtain appendix as, if I have done even a half-decent job, it should be a somewhat mind-blowing revelation, though again, all-the-more mind-blowing if you have spent considerable time playing in ignorance beforehand!

So... on to Creating a Character we go. Onward ho!

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