In a recent leaked document, Wizards of the Coast has apparently threatened to revoke the Open Gaming License version 1.0a by stating that it will become "unauthorized." From what some lawyers are saying on the Internet, because the OGL 1.0a license does not use the magic word "irrevocable," this is actually something that WotC may actually be able to do.
Ryan Dancey, the architect of the OGL, has stated on Enworld that he disagrees that the license is revocable, but until a court makes a ruling (should it ever come to that) we can't really be sure. And now that Wizards of the Coast has threatened to do it, until it does go to court or it's revised to be explicit, the OGL is Schroedinger's license.
It doesn't much matter whether the leaked documents are accurate and whether the threat is possible or not. Through the threat of revocation (or "deauthorization") followed by silence, Wizards of the Coast has demonstrated that neither community nor legal agreements matter to Hasbro. They're willing to let a 20 year old legal license be threatened. If the leaks are false, then from a defender of an open culture, I'd have expected an immediate statement condemning it. Regardless of the extent of this threat, Wizards of the Coast looks less trustworthy today. And unfortunately, the text of the Open Gaming License 1.0a is copyright by Wizards of the Coast, so with their threats even the license suddenly feels less reliable.
Open culture is, despite what business and legal systems assert, our default reality. But the corporate world doesn't operate on handshake agreements and licenses that read "just be cool." The Open Gaming License 1.0a has served the tabletop roleplaying community for 20 years now, but recently Wizards of the Coast has hinted that they intend to assert their ownership of the text of that license by declaring it "unauthorized." What that means is unclear, but one thing that's evident is that, despite the goodwill they've earned during their 5e work, the latest iteration of Wizards of the Coast is not your gaming buddy.
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Luckily there are other open licenses out there, and I've got extensive experience with two of them. I'm not a lawyer, I've never been to court over licensing, so don't take my thoughts on licensing as legal advice.
Before getting to licenses, consider the meaning of "copyright."
Copyright is the "right to copy." In many countries, copyright is an innate trait you get whenever you create something. When you create a thing, you have copyright over it. As I understand it, some countries don't even let you relinquish that. You created something. It's yours.
Copyright is not a license. Copyright essentially says nobody but you has the right to the content you've created. Obviously in real life we don't live by that rule, because we do things like write blog posts on the Internet. And it's because we're humans and we like to share the stuff we create that we invented "licenses." A license helps you, as a content creator, explain why and in what way you're sharing your content.
In other words, a license sits on top of copyright, adding terms and conditions to your innate right to your own content.
The Creative Commons license is an irrevocable and modular license. It recognizes that not all content creators or projects need the exact same protections. There are a few different components you can choose between when declaring your Creative Commons license:
The non-profit organization that manages Creative Commons has a great license chooser at creativecommons.org/choose.
Unlike the Open Gaming License, the text of a Creative Commons license is itself licensed under the Creative Commons Zero license, which means that even if an organization tried to "unauthorize" the Creative Commons licenses, you can legally copy and paste the text of the license into your own document, give it a new title, and continue using it as-is. By contrast, the text of the Open Gaming License is copyright by Wizards of the Coast, so to create a new open license for gaming, somebody has to hire a lawyer to write original text that states the same thing. You don't own the Open Gaming License. You own the Creative Commons License.
To use the Creative Commons license, step through the license chooser. Scroll down to the Have a web page? section and select and copy the licensing statement. For example:
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Paste that statement near the copyright statement of your work, and you've just licensed your content.
The closest thing to Open Gaming License 1.0a is CC BY-SA, which stipulates that other people can use your work as long as they credit you, and share their work as you have shared your work. The one significant difference is that there's no concept of product identity in the Creative Commons License. However, as the copyright holder of anything you create, you are permitted to qualify how a license does and does not apply.
For instance, say you'd created an RPG product that takes place on the planet Kana, created by the goddess Chuzrae, and that features a powerful magical spell called Innazdrith's Bombastic Bubble. You're happy for people to use the game rules you've created, but you have big ideas for how the world is going to develop, so you want to maintain control of the story elements. So in your licensing section, you could write:
With the exception of place names and the names of gods, you may use this book's contents under the terms of the Creative Commons Attribution-ShareAlike 4.0 International License.
That means I could write a book compatible with your game, and I could even use the spell name Innazdrith's Bombastic Bubble in my material. However, I could not use your world Kana or its creator goddess Chuzrae.
You can restrict or unrestrict as much of your material as you want. Maybe you don't want people using the spell name. In that case, write something like this:
With the exception of place names, the names of gods, or spell names, you may use this book's contents under the terms of the Creative Commons Attribution-ShareAlike 4.0 International License.
The important thing is to be clear in your declaration. Don't use vague terminology like "...the names of any of the important gods (but minor ones are OK)." Follow the example of product identity definitions publishers have used for the Open Gaming License. Or, for maximum clarity, publish a system reference document in which everything can be used under the Creative Commons license, and reserve all the special names and cool fiction for commercial version.
The GNU Free Documentation license comes from the world of technical documentation, like software manuals. Game rules are essentially the "code" of a game written in natural language, so there's more in common here than you might at first think. The GNU Free Documentation license is quite a modern license, acknowledging that many documents exist only online as wiki pages, or that they may also be licensed under a Creative Commons license. It's also got provisions for the difference between making a personal copy of a book and printing a book by the hundreds.
The 90s RPG Dead Earth was published using the GNU Free Documentation license, so using this license for tabletop RPG isn't entirely without precedence. To my knowledge, I don't know that it's ever gone to court, but other licenses by the non-profit GNU Foundation have widely and successfully been defended in court, so it's got a good pedigree.
As with Creative Commons, there's no concept of product identity in the GNU Free Documentation license. However, you could publish a system reference document that omits all the proper nouns and fictional elements that you didn't want other people to use.
To use the GNU Free Documentation license, visit gnu.org/licenses/fdl-1.3.txt and paste the license somewhere in your book.
Again, I'm not a lawyer, so this blog post is just based on experience of both myself and friends in the publishing and software industry.
The two licenses to avoid aren't really licenses at all. Don't release your work to the "public domain." The public domain sounds great, but in most legal jurisdictions, it's not actually defined. It's an adjective, not a noun. When you say your work is "in the public domain" in the US, for instance, it means you've relinquished any option to govern the future of that work. A company like Hasbro could grab a copy of your work, claim ownership of their copy, and make billions of dollars without so much as crediting you.
Also, don't not license your work. Saying that you don't want to bother with licensing is cool until it's not. The modern world is still coming to grips with what copyright means in the digital space. Clarity is essential, not only to protect yourself but to protect the people you want to be able to benefit from your hard work.
Yes, today it's cool for your friends to use your work. But what about when somebody takes their copy of it, declares ownership, and hires a lawyer to sue you or one of your friends for using "their" content?
It helps to view the copyright system as a minigame. There are rules, whether you like it or not, and there are people and companies out there whose nature it is to test the boundaries of those rules. It's just like in your weekly RPG game: You tell players it's against the rules of your world for them to climb the Godspire and claim divinity for themselves. What's the first thing they do? They spend the next 6 months trying to climb the Godspire.
License your work. Keep it independent, keep it open.