Atari800 - An open source 800, 800XL, 130XE and 5200 emulator for BeOS/x86, DOS, Linux, TOS, Unix, Windows, and Windows CE. - http://sourceforge.net/projects/atari800/
Atari800Win PLus - Windows port of Atari800 based on the original Atari800Win v2.5c sources. - http://atariarea.krap.pl/PLus/index_us.htm
Atari800MacX - A Mac OS X port of Atari800. - http://www.atarimac.com/atari800macx.php
Atari 800 Emulator for Windows - A step-by-step instruction for downloading and playing classic games in Atari800Win PLus. - http://ktchang.cnc.net/emulator/using_emulator.shtml
A8E - A freeware 800XL emulator for Windows/SDL. - http://www.zerstoerung.de/
EMUAPC - A commercial 130XE, 400, 65XE, 800, 800XL emulator for DOS and Windows. - http://www.komires.com/gb/page4.html
Rainbow/Mac - A MacOS X port by Richard Bannister of Rainbow. - http://www.bannister.org/software/rainbow.htm
Atari++ - An open source 130XL, 400, 400XL, 800, 800XL, and 5200 emulator for Unix and Windows. - http://www.math.tu-berlin.de/~thor/atari++/
Rainbow - Shareware Atari 400/800/800XL/130XE/5200 emulator for MacOS and Win32. - http://www.chrislam.co.uk/