Nestopia is an accuracy-focused emulator for the Nintendo Entertainment System/Famicom (and Famicom Disk System). It is a computer program that acts like a physical piece of hardware. In other words, this is a method of preserving videogame history, with the welcome side effect of allowing you to play NES games on a modern computer. Nestopia uses highly optimized cycle exact emulation, allowing it to run titles that rely on precise timing, many of which break under inferior emulators.
WWW: http://0ldsk00l.ca/nestopia/