One sentence: anything that might break. But I'm not saying this as blaming Linux about the brokedness. They're doing amazingly well for the huge amount of com

One sentence: anything that might break. But I'm not saying this as blaming Linux about the brokedness. They're doing amazingly well for the huge amount of combinations of hardware and software they're supporting. Apple, on the other hand, has decided to seriously limit the amount of hardware they support, which makes it a much easier effort to support those ones.