Nintendo Entertainment System
The Nintendo Entertainment System, or NES, was a video game console based around the MOS Technology 6502 processor. The NES utilized ROM cartridges for gameplay.
NES ROM images generally have the extension .NES.
The most usefull 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.