It is a Mega Pololu Shield, or RAMPS for short,designed to fit the entire electronics needed for a RepRap in one small package for low cost.
RAMPS interfaces an Arduino Mega with the powerful Arduino MEGA platform and has plenty room for expansion.
The modular design includes plug in for stepper drivers and extruder control electronics on an Arduino MEGA shield for easy service, part replacement, upgrade-ability and expansion.
Additionally, a number of Arduino expansion boards can be added to the system as long as the main RAMPS board is kept to the top of the stack.This board is mostly based on Adrian's Pololu_Electronics and work by Tonok. Copper etch resists methods suggested by Vik. Also inspired by Vik's work with EasyDrivers. circuit design based mostly on Adrian's Pololu_Electronics Joaz at RepRapSource.com supplied initial pin definitions and many design improvements. Much inspiration, suggestions, and ideas from Prusajr, Kliment, Maxbots, Rick, and many others in the RepRap community.