Gazell , or GZLL, is a proprietary packet radio protocol released by Nordic Semiconductor. The protocol defines a star topology with one HOST and up to seven DEVICE's. My experiments begin with their nRF51822.
In the GZLL protocol, the DEVICE's communicate only with the HOST. The DEVICE's can not communicate directly with other DEVICE's. The HOST can coordinate packets between DEVICE's. The HOST, however, can not initiate communications with the DEVICE's. It can only respond to a particular DEVICE in a return ACK packet. This can be limiting in many applications. But there are plenty of applications where this scheme can work well. The HOST or DEVICE's can be configured to coordinate packets with other connections that they may have access to. For example, WiFI, USB, BLE, etc.
Nordic provices the GZLL library as part of their SDK for their various ARM based SOC radio devices. Programming is done via the JTAG interface.
RFdigital provides access to the GZLL protocol as part of their library for their RFduino modules. The modules use the Nordic nRF51822 ARM based radios. The RFduino library resides in the Arduino IDE (1.5.x and 1.6.x). Programming the RFduino is done via a USB port interface. Using the Arduino IDE and serial/USB interface is about the easiest way to experiment with the GZLL protocol. Especially, if one does not need all the low level sophistication of the full blown SDK.