GnGeo
GnGeo is a software emulator for the Neo-Geo game platform that runs on Linux and Mac OS X. It is notable for the fact that it uses specialized cores to emulate the main processors, giving it a significant performance boost over more general emulators such as MAME.
As of 2006, GnGeo runs on three architectures, ARM, PowerPC, and x86. On x86 machines, it uses the Starscream core to emulate the Neo*Geo's Motorola 68k processor, and Raze to emulate the Z80. On ARM machines, it uses Cyclone and DrZ80 for their respective processors. All four of these emulation cores are optimized with assembly code. GnGeo doesn't have any machine code-optimized cores for the PowerPC platform, but instead uses the 68k core from Generator, which still gives it a useful level of performance. Even without optimizations, most games can run playably on a 300MHz G3.
GnGeo has been ported to the GP2X, allowing full-speed Neo-Geo gaming on the handheld, thanks to the optimized emulation cores. With some tweaks, it can be made to run on Mac OS X, though it does not integrate with the Aqua interface.