Well, there is only one piece of software available. You need to submit a form to become an iOS developer first and I believe the SDK is free. You pretty much have to use a MAC and it is all written in objective C language.
You need to be a pretty solid programmer to even think about getting started as it is not easy.
Once you go through all of that there is an APP approval process you have to pass. No junky apps or apps that crash a lot will be submitted. They also have a minimum standard you must meet in order to be approved.
I think all the info you need is here but, its not as simple as downloading a nice easy program and dragging and dropping stuff to make an app. Also there are some libraries you can purchase and use from within the SDK. Some are free but have stipulations about crediting them (like for icons and such) and others you have to pay for.
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