An MCP23008 I2C port expander is used to add 8 pins to the board for a total of 15. I2C is on pins GPIO2 and GPIO3. There is a solder jumper to change the address of the port expander if required. There is also a solder jumper to connect the expanders interrupt to GPIO4 if desired. In addition, we have added a 3.3v regulator that is automotive grade and can handle up to 16v.
This board is also completely useable with the existing RFduino "shields", just make sure the pins used on this one for the port expander (2 and 3) are not used on the shield in question. You can use the RFduino USB shield to program this board, an FTDI board, or just use another Arduino with the ATMEGA chip pulled out. Code is written in the normal Arduino IDE!!
There is a Adafruit Arduino library for this chip as well to make coding simple (this library is based on the 16 pin version of the chip, the MCP23017)!
Learn more about RFduino here: