https://marco.org/2007/06/18/everything-on-the-iphone-interacts-directly-with
Everything on the iPhone interacts directly with the kernel. …based on what I know, I don’t personally believe that there will ever be an open iPhone SDK.
— Anonymous Apple engineer to Ars Technica. I hope this is technically incorrect, since it would be quite an insult to the iPhone’s OS, and would ensure that it’s definitely not OS X or even something based on Mach.