Boycott Advance is a Nintendo Gameboy Advance emulator for Mac OS X.
EMUlaunch is simply a means to display file listings and artwork for your roms and emulators. It facilitates the opening of your games from one simple interface.
an open source emulator designed to emulate the Sega Genesis / Mega Drive console, a popular games machine produced in the early 1990s. It is a portable program written in C and has been ported to the Amiga, Macintosh, Windows and even pocket PCs such as the iPAQ and Cassiopeia
a Sega Genesis/Megadrive emulator for Mac OS X
KiGB is a free portable emulator for Gameboy, Gameboy Color and Super Gameboy for Windows, Linux, MS-DOS, and Mac OS X. Read more
(commercial) MagicEngine is a PC-Engine (TurboGrafx-16) console emulator: the famous console made by NEC back in '87.
MAME Library is an iPhoto-like front end / launcher for MAME OS X.
MAME OS X
MAME OS X is a native Mac OS X port of the popular MAME emulator. It is designed to take advantage of all the latest Mac OS X technologies, like Core Video and Core Image.
an arcade emulator currently running Sega System 32, Sega System 32 Multi and Sega Model 1 (not yet playable) games. The emulator is available for Windows, Linux and Mac
A n64 emulator designed to be multi-OS. It is developed on/for Linux but a Mac version is available.
a Neo Geo Pocket Colour emulator for Mac OS X
Nestopia is the current king of the NES emulation hill. It uses highly optimized cycle exact emulation, allowing it to run titles that rely on precise timing, many of which break under inferior emulators. This accurate emulation does come at a cost; Nestopia requires a minimum of a 600MHz machine for full speed; but if you have one, this the best available NES emulation for Mac. Read more
Oswan is a Bandai Wonderswan emulator for Mac OS X.
QMC2 is a Qt 4 based UNIX GUI frontend for SDLMAME and SDLMESS.
a freeware, open-source, portable emulator for the Sega Master System and Game Gear consoles
TGEmu is a freeware, open-source, portable emulator for the TurboGrafx-16 and PC-Engine consoles.
a Nintendo Virtual Boy emulator for Mac OS X