Meet the Crazyflie 2.0: an open flying development platform that lets you build and experiment with your own flying machine. It is compatible with Bluetooth enabled smartphones. Source code and hardware design are available for this product. You get a solderless kit which is easy to assemble.
The Crazyflie 2.0 supports expansion boards. It can be flown from an iOS or Android device. You get up to 7 minutes of battery life.