As a Kickstarter reward, the Gumshoe ruleset (used in games such as Trail of Cthulhu and Mutant City Blues) was released as an SRD. You can get it here:
<https://pelgranepress.com/index.php/tag/open-gumshoe/>

My legalese is poor, and I can't figure out if I'd be able to commercially publish a game I made using these rules as a basis. Thoughts?