For starters, I recommend my own developer docs . They are fairly robust and cover many areas, from user interface consistency to small things.
For Mac development, Xcode is the way to go. It handles most of your needs: from building, testing, debugging, creating a user interface, and creating an installer.
The Mac OSX kernel API works with C, C ++, Objective-C, Python, and IIRC Ruby. If you want to move from Mac development to iOS development, then Obj-C is probably best.
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