One of the biggest features of the Galaxy Tab series (minus the OG Tab) is TouchWiz UX and its mini-app tray. In fact, it was difficult for me to get used to the Transformer Prime after having the Galaxy Tab 10.1 because I miss those little apps so much. For the uninitiated, mini-apps in Touchwiz UX are small "portable" applications that run in an independent window on top of the foreground application.
The TouchWiz UX mini-calculator
Of all the mini-apps, the calculator is among the most useful - who really wants to navigate away from the current application to use a full screen calculator (especially on a tablet)?