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I'm planning a project to create a retro-clone of a non-D&D game. The problem is that I specifically want to restate the mechanics of the game as faithfully as possible, but I'm not sure how to handle things like the skill list and skill names, spell names, a mechanically-central set of tables, and other things that are in the "grey" area of functional versus presentational and hence uncopyrightable versus protected expression.

To sort this out, I want to see what has worked in the past and what compromises other retro-clone authors have found necessary. I know there are lots of D&D retro-clones using the OGL, and lots of non-D&D games using the OGL that are not retro-clones. Unfortunately, most retro-clones solve the problem by either deriving presentational elements from another OGL'd set of rules (e.g. skill names from d20 SRD), using a different set of rules (e.g. Mutant Future is mechanically unlike Gamma World), or by getting a license/permission from the original game's author (e.g. ZeFRS has Zeb Cook's blessing). I don't have an OGL game to derive from, no license, and I don't want to change the mechanics unless absolutely necessary.

So, I'm looking for examples of other OGL games that:

  1. Clone a game's mechanics without deriving from an OGL set of rules
  2. Created by someone without rights to the original game
  3. Licensed under the OGL (so I can see how they pulled it off)

All the games listed in the Wikipedia article on Open Gaming are disqualified either by (1) or by both (1) & (2). In fact, the coverage of "retro-clones" in that very article makes "retro-clone" out to be synonymous with "D&D simulacrum".

It might be that the answer is "none exist", but even that would be useful information for me to move forward with.

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4 Answers

up vote 8 down vote accepted

There is DoubleZero: A Percentile-Based Modern Role Playing System by Berin Kinsman, a retroclone of the James Bond 007 RPG. It has mostly vanished from the net, but the SRD can still be found at http://livingfree.wikidot.com/doublezero-srd

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There are several.

4C System is a retroclone of TSR's Marvel Super Heroes (FASERIP). Unlicensed, and some subtle differences (including ditching the labels) but it works the same way.

There's a retroclone of Classic Traveller, I forget the name, but it's genericized (and not very well done, either). Separately, Mongoose Traveller is a pseudoclone of Classic Traveller, but is done under license. Note that none of the Mongoose Traveller OGL rules are copied from prior editions.

Mongoose Runequest is a pseduoclone of RuneQuest by Chaosium/Avalon Hill/Games Workshop. Legend is the same game, without the trademarks. Note that Mongoose acquired the Trademark for Runequest, then traded it to Greg Stafford for a license to use the setting. Neither had rights to the Chaosium game system, so Mongoose pseudocloned it - it's got major differences in character generation, minor ones elsewhere.

Mutant Future is a pseudoclone of one edition of Gamma World. It was adapted to be compatible with Labyrinth Lord, itself a D&D pseudoclone. Neither is done under license.

Starships and Spacemen 2E started out as a pseudoclone, but the project later acquired the rights to S&S 1E. It is actually a variant of Mutant Future, and is not the pseudoclone it originally appeared it would be.

Legends of the Ancient World is a close pseudoclone of The Fantasy Trip (Melee/Wizard/In The Labyrinth). It changes the way talents work (from reducing die-codes to adding points to the attribute), but is otherwise quite faithful. It's really a justification for them to release a bunch of TFT compatible modules. (And, if talents worked the same way as in TFT, it would be a retroclone, not a pseudoclone.)

None of these had parent games under the OGL, all of them are themselves released under the OGL. Three were licensed by the original IP holders (Mongoose's Runequest and Mongoose's Traveller, Goblinoid's Starships & Spacemen).


a game that is pretty compatible with it's inspiration, but has "improvements" in the mechanics, and is not written/published by the current owners of the emulated game.

a game that is as compatible as possible, essentially a rewritten version, only different enough to avoid copyright infringement.

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Goblinoid Games' GORE may be of interest to you, since it's basically a stripped-down version of Chaosium's Basic Roleplaying, which - as far as I know - doesn't have any OGL. Unfortunately, they don't seem to support the game anymore - at least it's nowhere to be found in the download section of GG's homepage.

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I downloaded a copy of GORE when I was first researching this. Unfortunately GORE fails (1): it's derived from the 2006 Mongoose RuneQuest SRD. –  SevenSidedDie Apr 14 '13 at 22:42
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From what I understand based on copyright law, at least in the US, comes from an interesting discussion. Here's exactly what someone over on 1km1kt.net (Chainsaw Aardvark) said when I was talking about a game:

Technically, you can't copyright game mechanics - otherwise we would all have to pay Milton-Bradly every time you specify "Roll 2d6" - but story elements are definitely yours.

The legalese for this can be found here:|


In particular:

Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles. Copyright protects only the particular manner of an author’s expression in literary, artistic, or musical form.

In short, you may not be able to find many good examples (though some have been given here), but legally you're fine and dandy so long as you don't use trademarked terms (for instance, when cloning D&D, you can't say "Action Points", though some mileage may vary on exactly how far these trademarks extend, if you enjoy lengthy and expensive court battles you'll probably lose).

In short, if you want to reboot your favorite system, feel free to, just don't steal text from it.

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I am not a lawyer, but I would be more cautious than this answer implies is necessary. It is true you can't copyright game mechanics, but if your game is clearly a "derivative work" of some other game, you have probably violated copyright even if you didn't copy a single word. Also remember that in many RPGs certain mechanics are tightly tied to the setting and copying those (even with paraphrasing) might caus an issue. When in doubt, it might be wise to speak to a lawyer. –  TimothyAWiseman Apr 15 '13 at 23:30
Good point. The copyright law isn't explicitly written with pen and paper roleplaying games in mind, so rulings could go either way, although I would be highly surprised if they did. –  Kyle Willey Apr 15 '13 at 23:36
Does not answer the question - he's asking for specific extant examples of this and the other possible approaches. –  mxyzplk Apr 16 '13 at 1:47
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