Here you are one of the easiest but most effective app to work creativity and imagination with your students: Splice. I created a Silent Film using this application. Later on, I posted on Youtube where my students had to guess where the film was located and then write a plot all togethere. 

https://www.youtube.com/watch?v=EG_kONWPiJ4

https://itunes.apple.com/us/app/splice-video-editor-free/id409838725?mt=8