FCEUX is a Nintendo Entertainment System (NES), Famicom, and Famicom Disk System (FDS) emulator. It supports both PAL (European) and NTSC (USA/JPN) modes. It supports both Windows and SDL versions for cross compatibility. The FCEUX concept is that of an "all in one" emulator that offers accurate emulation and the best options for both casual play and a variety of more advanced emulator functions. For advanced users, FCEUX offers tools for debugging, ROM-hacking, map making, tool-assisted movies, and Lua scripting. FCEUX is an evolution of the FCE Ultra emulator. FCEUX merges elements from FCEU Ultra, FCEU rerecording, FCEUXD, FCEUXDSP, FCEUXDSP CE, and FCEU-mm into a single branch of FCEU.
You can check the README in the subversion trunk for building instructions; or you can check this blog post for instructions on fetching the latest source from subversion and building it:http://blog.xannode.com/?p=14
Experimental OS X support available now available via homebrew [brew install homebrew]. Details here http://blog.xannode.com/?p=124