Form by Relative Wave is something you should try. This is a really great tool that is perfect for mocking up animated user interaction. It allows you to design motion and interaction and immediately see the results on your iPhone or iPad. You can even package the results as a file and share these with others. Best yet, it's free!
Form had been $80. Which is pricey enough to keep someone from buying it, unless they had a definite plan using it in mind. It was recently bought by Google and is now free.
While Form only works on Mac and iOS at the moment, It's my guess that it will be available for Android, and possibly Windows in the near future.