iNES by Marat Fayzullin, is, without a doubt the grandfather of the emulators. In the beginning, there was iNES... Pasofami came along shortly afterwards, but iNES was the pioneering Nintendo emulator, and brought many other emulators into the public light. Without it, we would have been lost to many of the old game console classics.

At the time (around 1995), iNES made barely playable a small selection of simpler NES games to the public. The sound was not great, the palette was not quite right, and the speed was not 100% (at least on my old P100), but every little advance at the time was invigorating to the community, and very exciting to me personally. People rallied around these emulators and formed the better part of the emulation community from this. iNES oftentimes finds itself forgotten to the likes of Nesticle, an emulator that had a more rapid development pace.

iNES brought several innovations to NES emulation. Besides being first, and making many pioneering advances technically, iNES established the format for NES ROM images that we see today. Previously, you saw ROMs that were in several pieces, depending on what information those peices contained. Pasofami, a Japanese emulator, could run those split images, but iNES (originally) could not. iNES came with a pile of tools to compile and fix the ROM images as they were. Many advances were made in the emulation, and many of the tools became obsolete for the what they needed to do.

iNES has progressed since it's neophyte days as an emulator, and now includes many features and bug fixes from before. The sound is good, the palette is dead on, and the compatibility is huge. It comes in several flavors, including binaries for Linux, BSD, Windows, Solaris, SunOS, AIX, and DEC Alpha. A Macintosh port is available from John Stiles. The Windows port is good, but is superceded by many other free NES emulators in compatibility and features (such as LoopyNES, Nesticle, and FWNES). iNES holds a place in the heart of those who have been around in the emulation scene. For these reasons, Marat is oftentimes considered the godfather of emulation. He also wrote fMSX (MSX emulator), Virtual Gameboy (Nintendo Gameboy emulator), ColEm (ColecoVision), and MasterGear (Sega Master System / Game Gear)

Some info taken from the iNES homepage at: