Reprap Arduino Mega Pololu Shield or RAMPS for short.
Full details of this open source hardware design can be found on the Reprap Wiki here:http://reprap.org/wiki/RAMPS_1.4
The 1.4 version is the latest version and incorporates the use of surface mount electronic components.
The shield is fully assembled. You will need to add an Arduino Mega 2560 or equivalent clone, the stepper driver modules and a power supply and you will have all the electronics necessary to drive a 3D printer.
The shield provides for:
Sockets for up to 5 Pololu style stepper drive modules. X, Y, and Z axes and 2 extruders.
3 channels of temperature sensing using 100k thermistors (not included) for heated bed, and 2 extruders
3 channels of MOSFET switched output for controlling extruder heating, hot bed heating and cooling fan speed.