Crazyradio PA is a long range open USB radio dongle based on the <nRF24LU1+> from Nordic Semiconductor. It features a 20dBm power amplifier, LNA and comes pre-programmed with Crazyflie compatible firmware. The power amplifier boosts the range, giving a range of more than 1km (line of sight) together with the Crazyflie 2.0 and above 2km Crazyradio PA to Crazyradio PA (line of sight).
The Crazyradio PA is not only for usage together with the Crazyflie and Crazyflie 2.0. Since it's an open project with firmware written from scratch and a Python API for usage it's great building block for systems that require longer range than WiFi and doesn't have the same requirements for bandwidth. The hardware comes shipped with the latest firmware as well as a bootloader that enables firmware upgrades via USB without any additional hardware needed.
The Crazyflie PA is compatible with the first generation of the Crazyflie, but will not give the same range increase as with the Crazyflie 2.0.