by Richard Bannister and the MESS Team
"MESS is a free emulator that can emulate a variety of systems. The current release (0.1) supports the NES, Sega Genesis/Megadrive, TRS-80, Colour Genie, and Colecovision. It is written in C and the source code is available for download. Ready-made binaries are available for a variety of systems. v0.2b4, a public beta version, is also available. This version also supports the Apple ][ Series, Atari800, Atari5200, Bally Astrocade, Kaypro 2x, PDP-1, Sega Master System/Game Gear, and Vectrex."