Steller is a mobile app for creating stories on your smartphone. It has a website as well though, slightly confusingly, you cannot create stories in it but only view them. There also appears to be no iPad only app.
Nonetheless it’s a good way of creating photoessays. You can also write text, either with photographs or in separate pages. Even better, it’s completely free.
Here’s my first Steller story.
No iphone app?