It’s a Software Development Kit. I assume you are wondering about the iPhone? You can download the kit off the Apple Website and use it to develop 3rd party applications to be used on the iPhone (like games and such). I am not technical, so I don’t know what kind of coding experience you would need or any of that, nor do I know if you can just pop the programs you made on the phone for your own personal use (I assume you could if you have a jailbroken one), but I know that Apple is expecting 3rd party developers to submit programs to them so that they can develop an apple repository for iPhone users (coming in June I hear). I understand that Apple will be extremely choosy in the programs they accept for the repository and I heard rumours that they will only allow certain programs at first and probably a very limited number. Unfortunately, I haven’t found (but I haven’t really looked either), the criteria that Apple is expecting for anyone submitting apps for consideration – but you can search the Apple website if you are interested further. Those programs chosen will require a initial $99 fee to be paid in order to be added and, if a fee is charged to the downloading iPhone user, Apple expects to get a percentage of that also. Hope that helps.