This is probably the smallest Arduino controller speically designed for controlling the servo. It features a 12 standard servo control capbility with Xbee socket which can be used to control helicopter or UAV via the Xbee link. The feather weight (7.5g) make it an ideal controller for those application that has limited payload. The build in regulator is allow the input voltage vary from 3.5-8V which fits the most power supply without any modification.
This DFRoobot relay shield V2.1 is a completely new desgin which is capable of controlling 4 relays. The max switching power could be DC 90W or AC 360VA. It could be directly controlled by Arduino/DFRduino through digital IOs with external 9v supply. With buildin xbee type socket, it can be wirelessly controlled via Xbee/bluetooth/WPM. Make it an ideal solution for home automation and robotics purpose.