This is taken directly from the software FAQ.

"Q: What is different if I use the d20 System License?

A: In addition to following all the rules of the OGL for any Open Content you use, the d20 System Guide doesn't let you describe the process for creating a character, describe the process for applying experience to a character, and cannot be an interactive game.

NOTE: Please pay attention to the section of the license that prohibits a Covered Product from being an interactive game. It is not enough to say your product isn't a game; the license gives a definition for what is considered to constitute an interactive game.

"Interactive Game": means a piece of software that is designed to accept inputs from human players or their agents, and use rules to resolve the success or failure of those inputs, and return some indication of the results of those inputs to the users.

This includes the obvious examples of attacking in combat, saving throws, and skill checks, but also includes dice rolling for character ability scores and hit points and rolling for damage. Why? Because in the d20 System a higher number is almost always better. Rolling an 18 for strength is obviously a preferable outcome to rolling a 3. In any circumstance where one outcome is quantifiably better than another is considered by Wizards to be an indication of success or failure; the software cannot perform these kinds of operations without breaching the license."

I think this means that you cannot create a computer game using the d20 rulesystem even though you do not mention d20 anywhere.

No, that just says that interactive games aren't permitted under the license, and that they define what is a game by looking at how you're processing rules and the like. Preventing you from using that license is not the same as saying that you are now infringing any other law. Providing you never endeavoured to accept that license in the first place, there's no problem.

A license is just a document that gives you some benefits in return for you adhering to some restrictions. The benefits of the d20 license are that "you are hereby granted the [...] license to use the d20 System trademark logos, the d20 System trademark, and certain other trademarks and copyrights". The license makes no mention of rules or mechanics because it has very little to do with the rules and mechanics, only the text that describes those rules and the logos that identify such books.

So do you think it would be safe to use the mechanics of d20 and modify it for our need? Just as long as we dont mention d20 anywhere? It would have made things a lot easier since the campain is based on the d20 mechanics.

You'll be safe using the mechanics, but bear in mind that specialist terms like "thac0" and any text from the rulebook may be restricted. Stick to generic concepts when describing things. Basically, there should be nothing visible that makes it look like you're trying to sell your product based on being derived from the d20 system.

Thanks. This is great to hear. This is not going to be a commercial title, just a hobby project my friend and I will be working on. It would have been sad if the game got popular and WoTC came and said "Close this project or we'll sue you!".

I'm going to have to disagree with Kylotan here. Trying to use the d20 rules and "hide" the fact that you are using them is a bad idea. Kylotan (and others), I think, have the wrong idea of what the d20 rules are. It has very little to do with a 20-sided die. Basically d20, for all intents and purposes, is dungeons and dragons 3rd edition. Rather, Dungeons and Dragons is a subset of d20. The d20 rules include all of the dnd classes, the monsters, the magic items, the equipment, etc. It's not a case of WotC trying to patent the rolling of a die or a few specific rules. All of the rule books (and the SRD) are copyrighted material and intellectual property. Yes, you can use the basic idea of die-rolling and basic rpg staples like elves and wizards, etc., but no, you cannot make a new game based on dnd or d20 without acquiring a legitimate license.

makeshiftwings : Thats what I thought. But we are not planning on using the races, classes or monsters. We are only thinking of using the underlying core system. I always thought that would be illigal, but some people here have given me hope :)

But since we are only a small team, and not going to make any money on this project, I doubt WotC will be against it. Just using the core system as a reference and apply all our house-rules.

You could try it, but it's still risky in my opinion. You need to make sure you never, ever actually say "My game is based on d20" anywhere on your website or similar places. And if you're not going to be OGL-compatible and do it all without any license, I'd be careful about using the same names for skills, feats, weapons, spells, etc.

Also, you should know it's not just a matter of WotC thinking you're a small company and not a threat; there's the matter of "legal precedent" and things like that, where if WotC finds out someone else is making a game based on d20 and dnd, they legally have to put in an effort to shut you down, otherwise they can get sued by Interplay (who bought the exclusive rights to make d20 games), and face other legal trouble down the road for not properly enforcing their copyrights.

Quote: Original post by makeshiftwings
Trying to use the d20 rules and "hide" the fact that you are using them is a bad idea.
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It's not a case of WotC trying to patent the rolling of a die or a few specific rules. All of the rule books (and the SRD) are copyrighted material and intellectual property.

I think we're saying the same thing actually, so maybe I didn't make myself clear before. The things I am claiming are not covered by copyright, trademark, or patent law are the mechanics. In other words, the thac0 vs. armor class resolution is not protected in any form, although it might well be that the term 'thac0' is. On the borderline are things where a rule can be expressed in terms of an equation, which would not be protectable, versus rules expressed as a lookup table, which can obviously only be used by copying that table, leading to potential copyright infringement, depending on whether the contents of the table constitute a creative work or not.

To be explicit, quoting TITLE 17, CHAPTER 1, Sec. 102(b) relating to copyrights in the US, "In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work". I hope that clarifies things a little.

I will add however that you are right on another important account, and that is that even freeware and not-for-profit entities are just as liable when there are intellectual property issues.