The ACEduino Mega 2560 has a longer board that measures, 4 inches by 2.1 inches.  But the arrangement of the female headers/male headers on the boards with respect to the microcontroller pin outs corresponds to the available pins. Thus, shields used for the ACEduino can also be used for the MEGA without modifications.

Features:

Microcontroller: Atmel, ATmega2560-16AU
Input Voltage: recommended 7-12V DC
Input Voltage: operating limits 6 (min) – 20V (max) DC
Digital I/O Pins 54 of which 14 provide PWM output
Analog Input Pins 16
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory of the ATmega2560-16AU, 256 KB of which 4 KB used by boot loader
SRAM of the ATmega2560-16AU 8 KB
EEPROM of the ATmega2560-16AU  4 KB
Clock Speed 16 MHz  from Crystal Oscillator
UARTs  hardware serial ports 4
USB connection for serial communication to a computer and to allow in
circuit programming of the microcontroller through the computer
External power supply jack for wall adapter
In-Circuit Serial Programming ICSP header
Reset Switch