The Moto X allows you to quickly access the camera application by flipping your wrist twice. This is invaluable for anyone with kids or anyone who just likes to capture rare moments in general. With the Xposed Framework and a certain module you can use this native gesture to open other apps. Twisty Switch is the Xposed Module by developer "dymmeh" which allows you to choose your own app to be opened by the Wrist Twisting Gesture. It looks like you will only be able to enable apps that are in your app drawer for now. This can be a bit of a security risk too since it totally bypasses the lockscreen when opening the particular app. Head to the link below for the download.
Via XDA
Via XDA