Games like Call of Cthulhu, RuneQuest and SuperWorld from Chaosium use the Basic Roleplaying System (BRP).
Now, your RPG could also use BRP. Chaosium has released a systems reference document which sets out those rules you can include in your own game.
The Open Game License (OGL) explains what is allowed and what is not. Following the rules of the OGL means that you can use the Basic Roleplaying rules engine in your own roleplaying games, sell and earn money from those games, without first needing permission from Chaosium or paying them any royalties.
Gamers familiar with the latest versions of Dungeons & Dragons will know how this works.
There are official D&D products that come from Wizards of the Coast, but there’s also a vast ecosystem of third-party products that use the rules, fit snuggly into a game of D&D but aren’t allowed to describe themselves as D&D. These games often talk about ‘the world’s most popular roleplaying game’ instead, or just use ‘5th edition’.
The OGL for Chaosium’s BRP is different, though. Just because you’ve read and understood Wizards of the Coast’s OGL does not mean you know what Chaosium is asking.
For example, you can’t use BRP if you have sanity mechanics that a very similar to Call of Cthulhu. Those are out of scope. Nor can you use a Glory system similar to King Arthur Pendragon.
You can read more, and download in full, Chaosium’s BRP – System Reference Document here.
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