Propel 1890 is a free utility and tool application developed by Rooftop Group USA Inc. for iPhone users. It is designed to control four axis aircraft through WiFi protocol. The app has a simple interface that allows users to remotely control the aircraft using their iPhone, iPad, or iPod.

One of the best features of the app is the ability to display real-time video taken by the aircraft's camera. The video data is transmitted via 2.4G WiFi protocol, which ensures a stable and reliable connection. Users can also take photos and record videos on their devices while controlling the aircraft.

In addition, the app supports VR function, which enhances the user experience by providing a more immersive view of the aircraft's surroundings. Another useful feature is the continuous and delay taking photo mode. Overall, Propel 1890 is a great app for those who want to control and explore their four axis aircraft through their iPhone devices.