Separator
If your applications requires to separate different parts of GUI elements, you can use separator for this. AppInventor does not have this by default, so you have to work-a-round it. Here is how: To create a separator in your android app, just use simple Label component. Set BackgroundColor to black (or whatever else that fits your theme), empty the text field, width- Fill parent, and Height- 1 pixel. And here you have a separator in your application.