Crazyflie is an open source nano quadcopter from Bitcraze
The Crazyflie nano quadcopter is part of the Crazyflie platform which consists of several different components, like the Crazyradio (a USB radio dongle), the development environment and the host PC and mobile applications. It is developed by Bitcraze.
It is not designed to be a consumer product, but rather an open source platform for development, teaching, research or experimentation.
Documentation can be found in the wiki. The source code for the firmware and the client applications can be found on GitHub.