Feature, in fact, define core functionality of your app. iBuildApp provides more than 30 different features (see Features page: http://ibuildapp.com/features/).
Each feature is customizable in terms of design and content. I.e for Calculator feature you set up variables, constants, values, formula and color scheme. To manage widgets within your app, open up the Edit section and click "Replace feature" button:
After that you will be given a list of available feature that you can add to your application.
Choose needed feature and our system would replace it automatically for you.
Note: it is not possible to recover any data lost during the replacing process (until you have made a backup of your application).