Nintendo Entertainment System
The Nintendo Entertainment System, or NES, was a video game console based around the NMOS Technology 6502. The custom chip was produced by Ricoh, and named the 2A03 processor. The NES utilized ROM cartridges for gameplay.
The most useful NES emulator for hacking purposes is FCEUXD SP which includes a Trace Logger, a built-in Hex Editor, a Name Table Viewer, Code/Data Logger, Inline Assembler, and Game Genie Decoder/Encoder, PPU Viewer, and a Debugger with Conditional Breakpoints and Symbolic Debugging.
Schematics of an old copier are available here.
The IO-56 is a homemade NES Dumper by Pascal. Felber.