GMR is the abbreviation of General Mobile Robot controller. It's an integrated circuit board specifically designed for home robot platforms, such as HCR (Home Care Robot).
In this integrated version of GMR, you will need three microncontrollers (MCUs): two Arduino Nano/Dream Nano and one Arduino Mega/Arduino Mega ADK, wherein one Nano works as motor control and data acquisition, and the other one as the ultrasonic sensor driver. The Arduino Mega/Mega ADK works as the main controller board to collect and transimit data as well as to drive other expansion modules, there is also a micro sd card slot for Mega ADK. There are two extra wireless communication plots that can be plugged with Xbee, Bluetooth and other communication modules. The GMR has intergrated 8 I/O ports, 8 analog ports and 3 I2C interfaces as input and output for Mega ADK. As for the part for nano on the GMR, the board also has special ports for motor drive and an adjustable knob for voltage output.
Note: The lastest version has been compatible with V3 & V4.