PbtA is not generically under any version of Creative Commons. Vincent and Meg, creators of Apocalypse World (the first PbtA game), have encouraged people to make games inspired by theirs because they know mechanics can’t be copyrighted. Their formal statement is
here.
Several PbtA games do carry a CC-BY license; Dungeon World and Thirsty Sword Lesbians are two that I know of. I think it’s important to be specific here so that people don’t assume that (say) the Avatar PbtA game is under an open license.
The same note applies to all of the CC-BY licensed games — derivatives may not be open licensed.
GUMSHOE is dual licensed under both the OGL and CC-BY. So is FATE.
Rowan, Rook, and Decard released their Resistance Toolbox under CC-BY. It’s the system that powers Heart and Spire.
Trophy has a CC-BY SRD. 2400 (minimalist flexible system) has a CC-BY SRD.
Fari Games is not exhaustive but it’s pretty good.