Android: Everyone hates it when they go through a routine app update only to discover the new version changed everything for the worse. Appwererabbit solves this by saving old versions automatically.
As soon as you get an update to any app you download from the Play Store, Appwererabbit makes a copy of your current APK file before updating to the new one. The app differs from Titanium Backup in that it doesn't save your actual app data, just the APK file itself. Also, if the app you're using relies on old server-side code, it could present some problems.
Nevertheless, if you're looking for a little insurance in case you don't care for a new version (something that's not exactly uncommon), Appwererabbit has you covered.