From the Instructable:

Main Features:

• X mode flying
• MPU-6000 gyro & accelerometer sensor for flight stabilization
• USB battery recharging on the transmitter, the copter plugs into the transmitter to recharge
• When the copter plugs into the transmitter, the user can synchronize to a random radio frequency
• Controlled using a Wii Classic Controller, which plugs into the transmitter
• Running a modified MultiWii firmware, which is open source, written with Arduino and Processing

Dimension Specs:

• Square center body is 1.5" by 1.5"
• Propellers are about 45mm in diameter
• Diagonal motor to motor distance is 110mm
• Motors are supposedly "X-Twin" spare motors, they come with the propellers

Electrical Specs:

• Flight battery is a single Li-poly cell, 3.7V, 350mAH, 20C
• Controller battery is a single Li-ion cell, 3.7V, 1000mAH
• Uses ATmega128RFA1 microcontroller for both copter and transmitter
• This particular ATmega has a built-in 2.4GHz transceiver, 16 possible channels, 250kbit/s or 2mbit/s max depending on the standard being used.

Design Highlights:

• The "arms" and "body" are connected by locking slots, making them easy to build and repair
• Motors slide right into the arm
• Two layer 1.6mm thick FR4 PCB used (this is the default for a lot of PCB manufactures), the components are all on a single side (easy to assemble)
• All open source project, schematics + PCB + code all available. Heavy use of Arduino and Zigduino involved.