Bochs
Bochs is a portable x86 PC emulation software package that emulates enough of the x86 CPU, related AT hardware, and BIOS to run Windows, Linux, *BSD, Minix, and other OS's, all on your workstation. I tried it out and with three clicks you have a running Linux box.
http://sourceforge.net/projects/bochs/
Bochs Tools, http://www.bablokb.de/bochs-tools/
Qemu
There has been some work done by Pierre d'Herbemont lately on Qemu to run on OS X . QEMU is a fast processor emulator using dynamic translation to achieve good emulation speed. QEMU is also available for Windows host computers.
http://mail.gnu.org/archive/html/qemu-deve...2/msg00104.html
http://cvs.opendarwin.org/index.cgi/projec...e/related/qemu/
http://am.xs4all.nl/phpwiki/index.php/Qemu
http://fabrice.bellard.free.fr/qemu/
http://www.h7.dion.ne.jp/~qemu-win/
Qemu GUI for Windows, http://perso.wanadoo.es/comike/
Qemu GUI for K, http://kqemu.sourceforge.net
Qemu GUI for Mac OS X, http://cordney.com/QemuX
Morphix on Qemu on Windows
START qemu.exe -L . -m 128 -cdrom MorphixCombined?-LightGUI?-0.4-1.iso -enable-audio -localtime
Qemu Networking Howto, http://lists.gnu.org/archive/html/qemu-dev...9/msg00150.html
Qemu User Forum, http://www.dad-answers.com/qemu-forum/
SkyOS? and Qemu, http://laxity.s4.cybton.com/skyos/
Qemu Tips, http://www.linuxforen.de/forums/showpost.p...170&postcount=6
Qemu on OSX
http://stegefin.free.fr/qemu
http://cordney.com/mymacintosh/doku.php?id=wiki:qemu
Qemu and Knoppix
http://unit.aist.go.jp/it/knoppix/qemu/index-en.html
Debian for Qemu
How to make an image with dd, http://lists.gnu.org/archive/html/qemu-dev...9/msg00391.html
http://www.freeoszoo.org/~blacknoz/
See below:
http://lists.gnu.org/archive/html/qemu-dev...1/msg00018.html

> Hi guys,
>
> Here's the Debian Woody system that I've been playing around with. It's
> about a 50Mb download that decompresses to a (mostly empty) 500Mb disk
> image. It runs a 2.4.22 kernel, and there's a few useful/interesting
> utilities on there, like nbench, and ssh and vsftpd servers. Networking
> is set up with the emulated NIC configured to 192.168.2.2, and apt
> configured to use a proxy running on 192.168.2.1. The kernel has vga16fb
> and serial console support, but lilo is configured to boot the system
> with a standard VGA text console.
>
> My experience playing around wtih this image has been pretty good,
> though I regularly experience seemingly random crashes.
>
> You can grab it here:
> http://gir.eclinic.com.au/~lsd/qemu/minideb.img.bz2
> The root password is "rootme".
>
> Thanks
> Leigh

PearPC
PearPC - PowerPC? Architecture Emulator can be found on sourceforge too.
http://pearpc.sourceforge.net
Wine
Wine is an Open Source implementation of the Windows API on top of X and Unix.
http://www.winehq.org