We propose, implement and evaluate the use of a smartphone application for real-time six-degrees-of-freedom user input. We show that our app-based approach achieves high accuracy and goes head-to-head with expensive externally tracked controllers. The strength of our application is that it is simple to implement and is highly accessible ' requiring only an of-the-shelf smartphone, without any external trackers, markers, or wearables. Due to its inside-out tracking and its automatic remapping algorithm, users can comfortably perform subtle 3D inputs everywhere (world-scale), without any spatial or postural limitations. For example, they can interact while standing, sitting or while having their hands down by their sides. Finally, we also show its use in a wide range of applications for 2D and 3D object manipulation, thereby demonstrating its suitability for diverse real-world scenarios.