itch.io

From several people saying they had actions taken against them for reproducing those on Kickstarters and other places. It's absolutely true that you can't copyright mechanics - but WotC has frequently went after people for reproducing their CC rules in text - I think the legal argument they fall behind is that the CC of D&D is a unique enough process to fall under their IP, but I'm not really clear on the specifics - I just see people saying its a thing Wizards have went after people for. See this comment thread for more;

https://theangrygm.com/save-vs-lawsuit-how-to-publish-dd-content/#comment-29263

While you may be technically correct, it's probably better for most creators to ere on the side of caution in these situations - no one wants their big project squashed by a C&D they can't afford to fight. 

thought process and abstraction cannot have a registered copyright (or patent, sorta), no, but you can still get sued for copying an idea. the legal idea is substantial similarity, and in the US (or countries part of the WIPO treaty) you can get sued for it, however rare. you can get literally sued for anything, and if you don't show up you lose automatically. what's more; the OGL is a trade agreement, a contract, and agreeing to it's terms supersedes on-the-street copyright code. so if you're using the OGL you agree to not do shit you would normally be able to otherwise, like how you cannot claim compatibility using proper nouns and are limited on the reproduction of procedure, etc. what WotC does and does not choose to enforce has no bearing on how it actually works.