Open20[TM], version 0.22
Below is a proposal for a new project, the Open20 system. The Open20
system is also known as "Open20[TM]", and we will the shorter "Open20"
minus the trademark within this work for clarity. The idea is to have
a simple, generic gaming structure that uses the ever-popular
ten-sided or twenty-sided dice,
but is open enough that publishers can customize it as they wish.
Premise of the Open20 system
- To promote a straightforward gaming system that anyone can use,
- To promote a gaming system so any gamer can walk into any Open20
game and be able to game right away due to an immediate understanding
of the basic rules.
To start, the Open20 License is as follows:
Anyone may use the Open20 System.
You may only call it "Open20[TM]" if you:
- include the version number of the Open20 document you are using, and
- do not modify any of the rules as given in that version of the
Open20 specification, and
- provide either a copy of the full Open20 specification, or provide
a link to the original (central) source for the Open20 specification.
You may, of course, add additional rules so long as they do not
supercede or overwrite the referenced Open20 rules.
The OpenSys License is as follows:
Anyone may use the OpenSys monicker.
You may only call it "OpenSys[TM]" if you:
- include the version number of the Open20 document you used as a reference
or basis, and
- provide either a copy of the full Open20 specification, or provide
a link to the original (central) source of the Open20 specification.
The "OpenSys" label is therefore an indication that concepts are similar
to Open20, but that the Open20 rigid standards are not applied.
Any Open20 or OpenSys license is 'frozen', which is to say it is not superseded
by later licenses. If you use "Open20 v0.22" and we later come up
with "Open20 v1.7" with new license terms, those new terms only
apply to "Open20 v1.7"-- you are free to keep using "Open20 v0.22"
with its original accompanying license terms. This provides security and
freedom for developers; you never have to worry about changing
licenses unless you wish to update to a later Open20 release set.
The Open20 specifications will be kept to a minimum in order that
creators and publishers have freedom to develop their own
settings and source material. At its heart, Open20 is simply a
standardized interaction and task-resolution system with a basic
skeleton for character creation and experience.
There are, in
some places, two options or conventions for dice rolling.
The suggested method, 'new school', requires only ten sided dice. The
'old school' method requires ten, twenty, six, and possible other-sided
dice.
Currently, the official repository for this "Open20 v0.22" is
www.rpg.net/news+reviews/columns/free20v0.html.
Now what?
To advance this, the system is based on the following meta-rules:
Roll between 1-20 (hence the name, Open20)
All resolutions and tasks can be resolved with roll between 1 and 20,
and higher is always better, either [GM's choice]:
- the sum of two ten-sided dice, 2d10 [new school], or
- a single roll of a twenty-sided die, 1d20 (which produces
a more erratic/random curve) [old school]
Rolls are based on a task difficulty level-- either against nature (a
GM-set difficulty based on 10=average) or against an opponent
(who gets to use their relevant skill as the basic number, plus any
bonuses and modifiers they may have). The PC trying the task then
gets to add their skill and any bonuses and modifiers plus a roll
of the dice to see if they beat that target number.
In general, the system is easiest with a level-based experience
system. This allows GMs to make a less arbitrary assessment
of PC fitness and threat difficulties, as well as providing a
handy ruler for characer advancement. And frankly, CRPGs have
made 'leveling up' a potent part of the RPG process.
Expandability
As should be obvious, Open20 is a rules framework. Anyone can
add their own expansions, and we hope to publish some of them within
this column. Each module will likely have its own additional license,
as desired by the author, and will of course also be bound by
conventional copyright and trademark requirements. One can envision
a campaign simply defined as "Open20 v1.1 new school using the 'High Tech Earth'
rules by Jane Writer." Easily described, and all players instantly
know what they are about to play.
Basic Natural Attributes
Player Characters (PCs) possess basic Attributes (Str/Dex etc), generated using
a distribution between 1 and 20. Two methods are allowed:
- Roll 2d10 and add; that's your number. This creates a triangle
distribution, with a strong tendency towards high or low. [new school]
- Roll 4d6, drop the lowest die, then add. This makes a shifted
bell curve, with a bias towards higher number but less occurance of
very high or very low numbers, relative to the 2d10 method. [old school]
You can then add 1 point with experience,
reflecting self-improvement. Typically there are three to seven Attributes.
You roll the dice to generate the appropriate number of Attributes,
then assign the numbers to the Attributes as you wish.
| Physical: can be subspecified as |
| | Strength/Brawn |
| | Quickness/Coordination/Dexterity/Reflexes |
| | Toughness/Stamina/Constitution |
| Mental: can be subspecified as |
| | Intelligence/IQ/Smarts/Cunning/Thinking |
| | Wisdom/Intuition/Insight/Empathy/Feeling |
| Social: |
| | Appearance/Charisma/Cool/Status/Rank |
Unusual: (anywhere from zero to many of these may exist) |
| | Mana/Psi/Sanity |
These may be modified based on origin, race, or species.
Characters also have hit points, representing how often they can get
hit before they are unconscious or expire. In general, a character
gets 1 hit die (1d10) for each of their experience levels. Upon
advancing one level, they simply roll a d10 and add that to their
basic hit point total. This d10 roll may be modified by additional
class or attribute effects (for example, a character of class
'programmer' may only get 1d10-2 for hit die, reflecting slightly
less than heroic stature.) Any sum below 1 (due to penalties, etc)
is considered a '1', while any sum over 10 is valid and need not
be changed.
Careers and Classes
PCs have a schtick, something they do. This can be their career
choice, their character class, their military service branch,
and similar. This determines which skills you gain, and which
special abilities you may have. It also determines how you advance
as you get more experience in life.
Classes have either Levels, Ranks or CMI (Continuously Measureable
Improvement). Levels are
discrete increments of improvement, where (upon achieving the
requisite amount of experience) the PC improves. Ranks are
benchmarks (or quests)
which a character must achieve in order to advance.
CMI means that skills and other traits improve as they are used.
It is up to the GM which system to use; this document provides
full specifications for level-based usage because that allows
game creators an easier method of assessing the challenges
they present to the party.
Things You've Learned
Skills reflect what they can actually do, and affect rolls.
One learns skill based on the class path, and can then
apply those points to (duh) class-related skills. If you want a skill
that is outside of your chosen profession, they cost twice as much.
You can advance in fractional steps but can only spend whole points
(i.e. you can spend 1 point to get a half of a point in a skill).
In use, skills are always rounded down.
Special Abilities
PCs always have special abilities, one-time feats, or modifiers for
certain tasks. That's what makes them heroic, not just ordinary
folks. PCs start with 1 special ability and gain additional ones
as they increase in experience.
Task Resolution
Tasks are resolved by rolling a pair of 10-sided dice (2d10, "new school")
or a twenty-sided die (1d20, "old school") against
the given target number, adding in any skills or abilities or
modifiers as appropriate.
For 'man against nature', this roll is against a GM's best guess of
difficulty. In most cases, this is using a skill.
Then you just roll your 2d10 (or 1d20) and add your
Skill, versus a Task Difficulty Class/Challenge Number (DC).
This is a number set by GM or, if you're opposing someone in this,
based on their appropriate counter-skill. An average task has a
difficulty (DC) of 10.
For 'man against man' (aka combat), this target number is simply the
Defensive rating of that target, reflecting armor etc.
Thus combat is resolved just as an opposed skill check. This means
summing the attacker's relevant numbers: base attack skill, plus
any modifications due to strength, size, and special abilities.
Roll 2d10 (or 1d20) and add it. Compare this to the targets rating,
a base of 10 (average difficulty)
plus any modifications that the target may have due to armor,
speed, size, and special abilities.
If the roll succeeds (is higher than the target number), the target
inflicts damage as per their natural attack damage and associated
bonuses plus any weapons bonuses or effects.
Characters do not have to roll for situations where:
- the GM says they automatically succeed
- it's not life-threatening, they would succeed on a perfect
roll (of 20), and they spend extra time working on it [we call
this a 'free 20', just to be catchy and tie it in with our name], or
- it is life-threatening, they would succeed on an average
roll (of 10), and they spend extra time working on it unopposed.
(This means mostly man-versus-nature challenges of some danger
can be automatically defeated by proficient characters).
Experience
Characters that succeed against challenges and threats
will gain in experience, which lets them add new skills
or improve existing ones.
For Level-based experience, one can increase in a level of
experience using this formula: Points to next level =
1000*current level, or 1kP (kiloPoint) * current level.
For example, a level 3 character needs 3kP to get to level 4.
Experience is awarded based on how challenging the situation is.
Sum up the levels of the party, then compare with the
total (summed) levels of the threat. Add in 'bonus levels' for
special abilities possessed by the threat. Convert this to
a ratio, or a percentage (threat divided by PCs, threat/PCs).
Thus four level-3 PCs versus two level-2 monsters would be favoring
the PCs (4/12, thus 33%). If the two monsters were fire-breathing,
they'd brevet level 3 and thus the ratio would be 6-12, or 50%.
Also, track the average level of the PC party (e.g. 'level 3', in the above
case), for reasons we explain in a moment.
A typical challenge is one where the characters have a ratio of 25%.
This represents a challenge that the players are likely to win. Remember,
this is 'bread and butter' stuff since players suffer losses that carry over
between fights.
A difficult challenge is one of even odds, 1-1, or 100%; the PCs are likely to
win (because, all else being equal, a PC is more resourceful than a
general threat). A very difficult challenge is one where the odds are
3-1, or 300%, in favor of the threat.
Experience points are awarded based on the difficulty of the
challenge. A basic 25% challenge awards to the favored party, if it
wins, approximately 25% the amount needed to advance to the next
level, based on the average level of the party. This sum is split up
and distributed evenly by the number of PCs. This number is increased
if the odds were more difficult for the PCs.
If the odds were 75%, winning PCs get 75% of what would be needed
to advance, again then split among them.
Even odds is 100%, 3-1 odds are 300%, and thus awards three times as many
experience points if the PCs succeed. Etc etc. Sorry about having
math in this.
So say a party is a 1st-level programmer, a 2nd-level sysadmin, and
a 3rd-level manager. They defeat a challenge of four 2nd-level auditors
plus a 3rd-level taxmonster.
The party average level was (1+2+3)/3, or level-2; a level-2 character
would need 2*1kP=2kP points to advance. The party total
level was 6, versus 9 levels of auditors, thus it was 150% against the
party (tricky but not too bad!).
Having won, they got 150% * 2kP points, or 3kP points,
split 3 ways. With 1kP points each, the 1st-level programmer goes
up to level 2 (cost=1kP points), the 2nd-level sysadmin is halfway
to level 3 (1kP of the 2kP points needed), and the 3rd level manager
is only 1/3rd of the way to level 4 (1kP of 3kP pts).
Since experience point awards are then split among the party, this
means a typical party will have to have (number_of_characters * 4)
'bread and butter' encounters to "level up", or all advance one
level. They would only need (number_of_characters/3) very difficult
encounters to "level up", on average.
For individual PCs who achieve a new level, their character now improves.
Improvements and bonuses depend on the career/class path, and
also include +1 to the base 'attack' of the character and, as
mentioned earlier, plus extra points for attributes and new special abilities
at certain level stages.
These bonuses can be modified for
different career/class paths.
As an option, if you are using the Rank experience system (instead of Levels),
this means the GM has created goals or quests that must be
achieved for a character to improve. If you are using the CMI
system, then experience points are gathered and applied to
directly add to skills or gain new talents, as specified by
their character class. Typically, 100 experience points allows
the trait used to be increased by 1.
Extensibility
Users of this system are welcome to create their own worlds, adventures,
character creation rules, experience schemas, and other fun stuff.
Complete submissions may be sent to
free20@rpg.net,
and remain the copyright of the original author. Modifications to
the core Open20 rules, either by email or in the forum below, are
considered donations to the Open20 project and may be added into
future Open20 rules sets. If you do not wish your forum suggestions
to become part of Open20, you may assert your rights by stating so
in your post, with language similar to "Please do not add this to
Open20, but...".
Lineage
This system is heavily based on "Rules to Live By", originally created
in 1998 by Mike Young, John Kilgallon, and Sandy Antunes, and now
published by
Interactivies Ink.
That system had the essential structure of Open20: basic attributes,
skills that add to a base attribute and are resolved by adding a die
roll and comparing with a task or opposed skill, autosuccesses, plus
special abilities. And, of course, that you always want to
roll high.
The use of a scale of 1-20 is both because that is a trendy concept
now, and because it provides a really nice granularity to resolution
(as 1 'pip' represents a 5% chance).
The "new school" methods are there so that only ten-sided dice (d10)
are required. The use of 20-sided, 6-sided, and other
dice is provided for people who
prefer that sort of thing or who were raised on idiosyncratic versions
of D&D[TM].
In particular, the use of 2d10 to generate a more rounded 1-20
distribution was first stated by 'delor' in
this
forum post. A plot of various die rolling probabilities is
given here for rolling 2d10, rolling
3d6, and rolling 4d6 and subtracting the lowest.
The specific synonyms for the basic attributes are
derived from a half dozen different games over the past twenty years
plus a quick check with the thesaurus. The experience system was
created by Sandy Antunes during a fit of mathematical structuralism.
The inspiration for the Open20 License came from the BSD (Berkeley)
software license and the FUDGE[TM] license, in contrast to the GNU
Public License (GPL, which limits commercial derivation without
redistribution) and Open Gaming License (OGL, which provides
additional material but has proprietary limitations on usage).
The goal of the license is to allow open usage of Open20 for
personal or publishing use.
Open20 is a superset of minimal rules, under which players may enjoy a
wide variety of different games and settings. Rules are analogistic
to mathematical formulas, and thus while we are indebted to earlier
rules pioneers we are also happy to advance the state of the art with
Open20.
