Atari800MacX is Macintosh OS X Port of David Firth's Atari 800 Emulator. A full native Cocoa interface, including Preferences, Menus, File Associations, Help and more has been added.
Handy is an Atari Lynx Emulator.
Hatari is an Atari ST emulator for Linux, BSD, BeOS, Mac OS X and other systems that are supported by the SDL library. More precisely, Hatari is an adaption of the WinSTon source code to the SDL library, using the portable UAE CPU core instead of the original, non-portable assembler CPU core. Read more
an Atari 5200 emulator that has good sound emulation
an Atari 8-bit Emulator for Windows/MacOS/MacOS X
Sio2OSX is a peripheral emulator for the Atari 8-bit computers that allows the Atari computer to use an OSX based Macintosh as a disk drive, a cassette drive, and a printer. Sio2OSX peforms functions similar to APE or SIO2PC on Windows based computers.