The Christan-Wirth-School schedule notifier app for iOS, better known as CWS Informant for iOS. It tells you which of your lessons are moved an which are cancelled.
Your school is required to run an default Untis 2013 web interface for its schedule to do this. Change the URLs in the Fetcher.cs file and replace the string "CWS Informant" with the name you want in the whole project.
After that you're all set.
https://github.com/reknih/informant-droid Android
https://github.com/reknih/informant-wp Windows Phone