An emulator is a program that imitates another computer's hardware so closely that the old machine's software runs unchanged. Spectrum and C64 emulators circulated on public-domain disks in the early 1990s; by 1997 a PC could run most old computers and consoles. In 1999 UltraHLE, Connectix's Virtual Game Station and bleem! brought Nintendo and Sony into the argument, and a US appeals court ruled in 2000 that reverse engineering to build an emulator was fair use.
FCEUX is an open-source NES, Famicom and Famicom Disk System emulator first released in August 2008. It merged the many branches of FCE Ultra, itself grown from Bero's FCE of the late 1990s: one branch added the movie recording that tool-assisted speedruns need, others added a debugger and ROM-hacking tools. With Lua scripting and, from 2012, the TAS Editor, it became a standard tool for making tool-assisted runs of NES games.
Frode Solheim's FS-UAE, started in 2011, takes the emulation code of WinUAE and runs it on Windows, macOS and Linux, with a focus on games: a gamepad-friendly interface, a launcher tied to an online game database, and automatic WHDLoad installs.
Philip Kendall released the first version of Fuse in July 1999 as a ZX Spectrum emulator for Unix. Now also on Windows and macOS, it covers the Spectrum from the 16K to the +3, the Timex machines and the Pentagon and Scorpion clones, reproduces the ULA's memory contention and floating bus, and is free software under the GNU GPL.
The arcade emulator that became a record of the machines
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Nicola Salmoria released the Multiple Arcade Machine Emulator in February 1997 by merging his single-game arcade emulators. It aims to document how each machine works, not just to play its games. It absorbed the computer and console emulator MESS in 2015 and became free software under the BSD and GPL licences in 2016.
Mesen is an open-source NES and Famicom emulator written by a developer known as Sour, first released in February 2016. It became known for two things: passing the NES test programs its author tracked, and a debugger that shows what the console is doing on every scanline. Its SNES offshoot, Mesen-S, was folded into Mesen 2, which also covers the Game Boy, Game Boy Advance, PC Engine, Master System, Game Gear and WonderSwan. Since 2026 it has been maintained as a community edition under the NESdev organisation.
The PlayStation emulator that learned to do without Sony's BIOS
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PCSX is a PlayStation emulator for PCs, first released in September 2000 by a small volunteer team and published under the GPL in 2002. It began by needing a copy of the console's BIOS ROM and went on to imitate the BIOS itself. When its authors moved on to PCSX2, a PlayStation 2 emulator, others carried PCSX forward as PCSX-df, PCSX-Reloaded, PCSX ReARMed and PCSX-Redux, and a fork of PCSX ReARMed ended up inside Sony's own PlayStation Classic.
reSID is Dag Lem’s C++ SID emulation library. Its cycle-based model and documented measurements help players and full-machine emulators reproduce digital timing and analogue sound behaviour.
RetroArch began in May 2010 as SSNES, a small front end for the Super NES emulator bsnes. In 2012 it was renamed and built around libretro, an interface that lets any emulator packaged as a 'core' share one menu, one set of controls, shaders, save states and netplay. It reached Steam in September 2021.
ScummVM runs old games by reimplementing their engines rather than emulating an entire computer. Beginning with Ludvig Strigeus and Vincent Hamm’s SCUMM work in 2001, it grew into a collaborative project covering many engines. Players normally supply the original game data; an open-source interpreter does not make every supported game free.
VICE began in Finland in 1993 as X64, a Commodore 64 emulator for Unix workstations, and grew into a free, GPL-licensed emulator for most of Commodore's 8-bit line: the C64, C128, VIC-20, PET, Plus/4 and CBM-II. Its x64sc emulator, added in version 2.3 in the early 2010s, models the C64's video chip cycle by cycle.
UAE began in 1995 when Bernd Schmidt set out to emulate an Amiga, a job many people thought impossible, and was first nicknamed the unusable Amiga emulator. Its Windows port, WinUAE, dates from 1997 and has been led for most of its life by Toni Wilen, who added cycle-exact modes and support for every Amiga from the A1000 to the A4000 and CD32. Amiga Kickstart ROMs are still copyrighted, and Cloanto sells them licensed in Amiga Forever.
