What is it? Well its a emulator that can emulate Gameboy ROMS on PC. 2 do this u 1st need the orginal Gameboy cart. Then u need a E - Card Reader which u connect 2 ur PC Via USB. Then u insert the cart. Into the E - Card Reader which creates a GBA ROM file which can be opened on the PC using a emulator that can emulate GBA files. There are many but VisualBoy Advance is so far the best