Convergence
With each successive version of Mac OS X, Core Foundation includes a little more of the API from Foundation. For example, Leopard adds CFError, a CF class toll-free bridged with NSError, and Tiger brought CFAttributedString. Also, the Leopard release notes for Core Foundation contain a lot of mentions of Foundation: for example, the CFErrors that CFBundle can return all have error codes with NS* prefixes. (Didn't they make CF synonyms?)
I predict that Apple will one day work a great irony upon the world, by rewriting CF in Foundation.