Well to start with, there are patent problems. IANAL, but I presume Apple's thought long and hard about this. Then you have the licensing issues. To get the

Well to start with, there are patent problems. IANAL, but I presume Apple's thought long and hard about this. Then you have the licensing issues. To get the documentation, you need to clickwrap through the license that says you can't clone it. So it's not even like cleanroom engineering, where it's possible to legally document some assembly code you bought in a box. Then there's the real problem--Apple's SDKs are really quite good, all things considered. Cloning them would be very hard. There is some serious, complicated stuff going on under the hood, especially to make it performant. To say that a couple of clever Lisp hackers can clone it is to say that Apple could have built the API with a couple of clever hackers to begin with. It's to say that Jobs is stupid for having hundreds of people work on it.