I have a feeling it's time to repeat this:
You do not need a license or an SRD or OGL or anything like that to use any part of or even all of the mechanics from a #TTRPG in your own. You just can't copy them word for word. Rules are not copyrightable. It is, however, good manners to credit where you get your ideas from.
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@rivetgeek however using something like #creativecommons does make it easier for others to reuse your #cc #rpg because they *can* copy your words
@sgryphon Of course. And it helps with recognition because you've gotten explicit approval, provided you followed the license. Licenses or CC can also grant the use of things like logos or whatnot. But if you like a specific mechanic or rule (like say clocks, or hit points) you don't need that to use it in your own game.