The Cepheus Engine SRD has the following:
- Use of Product Identity: You agree not to Use any Product Identity, including as an indication as to compatibility, except as expressly licensed in another, independent Agreement with the owner of each element of that Product Identity. You agree not to indicate compatibility or co-adaptability with any Trademark or Registered Trademark in conjunction with a work containing Open Game Content except as expressly licensed in another, independent Agreement with the owner of such Trademark or Registered Trademark. The use of any Product Identity in Open Game Content does not constitute a challenge to the ownership of that Product Identity. The owner of any Product Identity used in Open Game Content shall retain all rights, title and interest in and to that Product Identity.
That’s part of the OGL, of course. It allows the SRD to include the following:
Publishing Your Own Materials
As you can see at the beginning of this System Reference Document, all of the text in this document is designated as Open Gaming Content, except for the titles of products published by Samardan Press, and the trademarks “Cepheus Engine” and “Samardan Press”.
This means you can copy whatever parts of the Cepheus Engine you want, add your own content, change the content around, and publish the result. Note that you will have to comply with the Open Gaming License, as reproduced at the end of this document. If you don’t mention any of the trademark elements, you don’t need to do anything else.
However, you can use the “Cepheus Engine” trademark, under certain circumstances, to indicate compatibility with this rules system. You have to follow the requirements of the Cepheus Engine Compatibility-Statement License (CSL), but if you do, you can state that your published material “is compatible with the rules of Cepheus Engine” or, “with the Cepheus Engine rules” or, “with the Cepheus Engine game.” Here are those requirements:
The Cepheus Engine Compatibility-Statement License (CSL)
1. You must state on the first page where you mention Cepheus Engine that “Cepheus Engine and Samardan Press are the trademarks of Jason “Flynn” Kemp,” and that you are not affiliated with Jason “Flynn” Kemp or Samardan Press™.
2. If you’re using the license to commit legal fraud, you forfeit the right to continue using the license: specifically, if you are claiming compatibility with the rules of Cepheus Engine, the claim must not constitute legal fraud, or fraud in the inducement, under the laws of the State of Texas. Note that this requirement is almost impossible to violate unintentionally—it’s largely intended to keep me out of trouble, not to restrict legitimate statements of compatibility.
3. You must comply with the terms of the OGL if the terms apply.
4. Your cover must include the words “House Rules” or “Variant Rules” or “Alternate Cepheus Engine Universe” near the title if the document is a full, free-standing game that includes modifications. Feel free to contact the author if you wish to use a different form of disclaimer.
5. Selling a full version of this game with your house rules incorporated into it is perfectly permissible, but you may not sell an effectively unchanged copy of the rules for money.
6. If your document is a private house rules document, not being sold for profit or general use, you may scan and use artwork (including the cover) from the printed version, published in print under the title of Cepheus Engine Core Rules, provided that the cover contains the words “House Rules,” near the title, and that the artists are appropriately credited.
7. Your rights under this CSL cannot be revoked, and are perpetual, unless you breach the terms of the license, in which case your rights terminate.
8. If you comply with the above, you may state that your resource is “for use with the Cepheus Engine Core Rules”, “compatible with the core rules of Cepheus Engine” or “with the Cepheus Engine Core Rules.”
This is the part that sucks about the OGL, it let’s someone swipe you with a separate license if you want to say basic facts about reality, such as, “this book works with Traveller RPG”. That is bullshit. It was bullshit when WotC didn’t want the Book of Erotic Fantasy saying it worked with D&D.
I’m not in the industry, but I’ve read it doesn’t make sense to use it if one wants to work in the industry, and yet so many hobbyist projects just embrace it. I suppose it does the heavy lifting? List after list of “free” games are OGL, very few CC or other open licenses.