Different kernel But fairly similar userland. Still shares some userland, but this is irrelevant. I would say that for most people, the API matters far more

Different kernel But fairly similar userland. Still shares some userland, but this is irrelevant. I would say that for most people, the API matters far more than the kernel implementing it. not open sourced http://www.opensource.apple.com http://www.opensource.apple.com has the kernel sources under "xnu". I don't think that substantially less is open sourced than e.g. for Android. look at how well their open sourced Darwin OS project is doing in terms of update and support The updates are fairly current (10.10.1 corresponds to the version of OS X shipped last fall), though there doesn't seem to be a very large community building on it.