CF was always (approximately) a multiplatform and open source subset of foundation (which is the thing this isn't). I think this is a superset and extension of the original core foundation under more favorable license terms though.
The "original" CF can be found here in various revisions tied to macos versions, complete with theoretically useful Linux makefiles and apple public source license files: https://opensource.apple.com/source/CF/
Compare, for example, these two versions of CFBase.c:
(Credentials: I worked on the swift Linux port and made an effort to use these very libraries before the swift project itself took on the task of porting CF to swift. While I was working on it we mostly just ifdef'd out everything to do with foundation when targeting Linux)
