What should be the good beginners project in cocoa to learn basics?

I had made iPlayer using NSSound c开发者_如何学运维lass which is a music application as my dummy project in cocoa. I need to make another project which will help me to understand the basics of cocoa in more detail.

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There is a three-part series on Building a Cocoa Calculator Application with XCode 3 for Mac on youtube:

• http://www.youtube.com/watch?v=GuUgrxU6pYU