Hi. I'm creating a roguelike together with a friend of mine based on a campain he has created for the d20 system (actually 2.ed, but converted to d20 once that came around). The problem is that you cannot use the d20 system in a computergame, so we are trying to find an alternative to d20. The prime requisite is that converting from d20 to this system and the other way around has to be very simple. We could create our own system, but this would involve hundreds of hours of testing and tweaking.. We hope that we could get away without this extra trouble. Does someone here know about a system like this that is freely available?

you can try d100 :)

seriously though, generate a random number between 1 and 100, and scale your rules (multiply by 5, if they are already set up for d20)...

i don't think it would matter though, really (IANAL). regardless of what they might claim, they can't possibly prevent anyone and everyone from using random numbers between 1 and 20. you just have to avoid claiming that it is a "d20 based game".

Mmmh, I ll assume you must be new at RPGs if you dont know other systems than DnD ?

From the top of my head :
the Chaosium system; used in Elric, Stormbringer, Call of Chtulhu,

the Warhammer system; the roleplaying system, obviously. Although the table top system is really just an extension of that. Or is it the other way around... :) ,

the GURPS system; the Generic Universal RolePlaying System, by Steve Jackson games. Used by the computer game Fallout.

the Storytelling system (I think) by White Wolf, used by the World of Darkness RPGs, used in the cRPG Vampire the Masquerade, and the soon to come out Vampire Bloodlines,

the Silhouette system by DreamPod 9, used in their RPGs (among others, Tribe 8 and Heavy Gear).

the Legend of the Five Rings system (the RPG created after the cardgame became so succesful).

And I know quite a few others but they would mean even less to you.

I suggest you look those up, especially the ones that give you free demo (yes, even pen and paper RPGs have free demos :) ) so you can get an idea of the few "styles" of systems out there.

I m pretty sure that as long as you are not claiming to use a given system, it doesnt really matter if you are using it or not.
It's all about the Logo really. And for a roguelike, honestly, would you really give a damn if it has a D20 stamp on it ???

And dont worry, the magic system from DnD is possibly the worst I have been given to see EVER in my 16 years of roleplaying, so you are not missing much.
Remember that D20 is mostly a commercial gimmick. It helps other roleplaying studios focus on creating content rather than have to recreate Yet Another RPG System from scratch.

Granted, that's what you want, but as I have pointed out, there have been other generic systems before. As for "open"...

Hope it helps :)

Wait a minute... you can't use d20 in a game? Have you looked over the Open Gaming Liscence? I mean, yeah, I haven't looked at it that closely either, but any (free) system in which you can sell someone else's intellectual property legally is probably going to allow computer games as well as print books...

I tried to start a project about 6 months ago using the d20 system. I was reading up on the licence agreement, and found out that you cannot use it in a computer game (need a licence).

ahw : Thanks for the great suggestions. I havent played any pen and paper rpg since 2.ed, but this really isnt just my project. I'm creating this together with a friend based on his campaign. We will but the roguelike on his website when it is playable, but since his world is based on the d20 rules, it would be a hard time converting every npc, monster etc. to a rulesystem that is very different.

I will have him look into the various systems you mentioned. I know that gurps is free to use like you want (think at least).

Thanks again for the helping post.

Quote: Original post by simhau
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I will have him look into the various systems you mentioned. I know that gurps is free to use like you want (think at least).

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This is not 100% true. You can download the GURPS rules from SJGames for free, but that does not mean the rules are Public Domain. Their online guide says that you must contact them for permission to use their IP before posting it in a game (scroll down about 3/4 of the way). You could email them and ask on the basis that your game will be free publicity for their game, but you do need their permission.

A system that I liked a lot was the HERO system (especially Fantasy Hero); other systems that I played a lot were RuneQuest, DragonQuest, Traveller, Rolemaster and Aftermath. I remember Aftermath being based on a D20 roll, so you might want to throw a quick look at that.

Incidentally, the whole dice rolling scheme is outdated considering the way computers work. Any good random number generator would create a number between 0 and 4294967295. Imagine playing a game thats d4294967295. The C formula d=floor((random()/4294967296.0)*20)+1; is what produces the whole 20 sided dice technique, so the 20 is really an arbitrary number. As for the DnD skillsets and classes and stuff, just make up your own stuff based on what the game would need.

Dice Rolling schemes in and of themselves aren't outdated. While a pseudo RNG will allow you to create things dice can't do, like an odd numbered range (say like rolling a d7), what's more important is the distribution of the discrete numbers within a certain range.

What do I mean? Well, in a d20 system, you have a flat distribution. I have as equal a chance of rolling a 1 as do of rolling a 10 or a 20. So my odds of rolling at the extremes are the same as my rolling a number at the median (or average). And this I think is the d20 system's greatest flaw and weakness. Because of the way the task resolution system works, it is as equally likely to do exceedingly well, to botch or to do something average.

In real life, most things have some sort of distribution curve that represents the odds of how something was done. The famous example is a grading curve. Generally, most people do average in school, while a small percent do very well, and a small percent do very poorly. This is the classic example of a bell curve. The problem with using a single die like the d20 system is that it can't replicate any distribution curve other than a flatline.

Multiple die rolling games can create different probability distributions. The new rage is to have a variable amount of dice that the character rolls, and there is a Target Number that you must (usually) match or roll higher than.

So really, dice are a nice way of looking at how to create probability distributions and figure out the odds of getting a certain result. The d20 system is incredibly simple, and offers no variety in creating a different probability distribution....all it can do is affect the characters chance of success or failure, but there is nothing it can do to effect what some games call Margins of Success. If you think of Margins of Success as deviations from the mean, a simple d20 roll will always have the same deviation no matter what. That's the advantage of using multiple dice mechanics. In computer terms you could do away with dice and just create your own probability functions.

Some friends of mine once came up with a system built around the Normal Distribution - basically, skill ranks or task difficulty translate to standard deviations from the mean and you roll d10s to generate a decimal value until you know you're above/below the threshhold value (found on standard statistical tables - or you could generate them from scratch if you really wanted to). Basically though, the underlying skill check mechanic isn't that important, what makes or breaks a system is the available skills, levelling mechanics, character types (races and classes in d20), items, monsters and so on into level and world design issues, which are generally separate from system design...

The simplest solution is to tweak d20 across the board, but the real copyright issues come in the content area rather than the underlying mechanics - if your skills/feats and character classes are the same as d20 equivalents, then you're more likely to suffer legal issues.