Here's a Christmas present to the App Inventor community, from MIT App Inventor team members Fu-Ming Shi and Wehua Li.
Christmas Yo Yo Fun is an App Inventor creation that you can
download for free from the Google Play store. It lets anyone create Christmas cards by filling in a form: you can include your own pictures and videos and you can send the card to your friends and family. Even better, it lets them create and send their own cards in turn. Yo Yo Fun was built with App Inventor 2. Its an example of the kinds of things you can do in App Inventor, by combining the fun of creating mobile apps with the power of the web.