For my U and I project i decided to make a tip calculator app. The widgets I used are text views, spinners, a rating bar, an edit text, and buttons. To get started you select the amount of people you want to split the bill with, then select the percentage for the tip, and then enter the total.
The app then calculates the total tip, the total tip per person, and the total each person should pay.
One lesson I learned is how to use the TableLayout. It was really easy to use and is much better for aligning data then using nested LinearLayouts.