first program in a new GUI framework

The usual hello world program I think is a terrible first program开发者_运维知识库 if you are trying to learn a new GUI framework. Putting some text onto a canvas skips the most important parts of a GUI framework: threading and callbacks. What are some of the first programs you write to learn a new GUI framework?

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A calculator is always a good idea:

• Simple UI
• You can take the windows calculator as an example UI
• Not very much work (as long as you don't want to support parentheses, but I guess you want to do only the UI anyway)