Ive been searching for an app like this ever since the first iPhone. It is very strange that Apple does not have this feature built-in already.
While this is a very good app, it does not make use of the +- volume buttons to take pictures or start/stop video recording. This really defeats the purpose of the ability to hold the phone vertically to take videos using only one hand.
The Tilt-to-zoom function is very clever. But, just like Apples inexplicable videocam design, there is no Pause function in Horizon either.
The "Tutorial" is essentially a joke. Other than that this is a pretty solid app that still has room to improve. Designers should try using this app with only one hand to figure out where improvements are needed.
Zen Archer about Horizon Camera