Chankast is an emulator for the Dreamcast system, it was the first Dreamcast emulator to run commercial games. This emulator is designed for Windows XP or 2003.

CuteBoy  is a GameBoy emulator (not GameBoy Color) for J2ME based on Mario GameBoy (TM) Emulator 0.2.4 by Carlos Hasan with good speed enhancements and many useful options.

Daedalus - An open-source N64 emulator is a Nintendo 64 emulator for Windows and the Sony PSP running homebrew demos and commercial games.

DeSmuME is a Nintendo DS emulator running homebrew demos and commercial games.

DOSBox DOS Emulater emulates a full x86 pc with sound and dos. Its main use is to run old application and games for dos on platforms which don't have dos (win2K, XP,  Linux, ...).

Bochs x86 PC emulator 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.

Gens is a win32/unix Sega Genesis / Sega CD / Sega 32X emulator.

Hoxs64 is Commodore 64 Emulator for  Windows 2000 / Windows XP / Windows Vista. The emulator substantially reproduces this legacy machine in minute detail.

Microsoft Virtual PC 2007 With this free Microsoft Virtual PC you can create and run one or more virtual machines, each its own operating system, on a single computer. This provides you with the flexibility to use different operating systems on one physical computer. The Microsoft Virtual PC 2007 supports the following operating system:  Windows Server 2003 x32 and x64 edition, Windows Vista 32 bit and 64 bit edition, Windows XP Professional x32 and x64 edition, Windows Server 2000, Windows NT4 Server and Windows NT4 Workstation, Windows 9x and some Linux edition.

NeutrinoSX2 (nSX2) is an open source emulator for the Play Station 2 platform. Just as the other emulators of its kind, its still under construction, so yeah it means that you can't run any commercial game with it. In order to run this emulator at its full speed with all the options turned on, you should have the recommended requirements: Intel Pentium 4 2.0GHz, 512MB RAM, Windows XP.

PCSX2 is a PlayStation 2 emulator for Windows and Linux, started by the same team that brought you PCSX (a Sony PlayStation 1 emulator). The PCSX2 project attempts to allow PS2 code to be executed on your computer, thus meaning you can put a PS2 DVD or CD into your computers drive, and boot it up!

Project64 is a Nintendo 64 emulator.

SATOURNE is SEGA SATURN emulator for Windows. The SATOURNE project attempts to allow SEGA STARURN code to be executed on your computer.

VirtualBox - innotek VirtualBox is a free family of powerful x86 virtualization products for enterprise and home user. High performance virtualization available as Open Source software under the terms of the GNU Public License (GPL). VirtualBox supports a large number of guest operating system including: Windows (NT 4.0, 2000, XP, Server 2003, Vista), DOS/Windows 3.x, Linux (2.4 and 2.6), and OpenBSD.

VisualBoyAdvance is a free GameBoy and GameBoyAdvance.

Yabause is a SEGA SATURN emulator for FreeBSD, GNU/LInux, Mac OS X and Wndows. Yabause support booting games using Saturn CDs and ISO files.

ZSNES is a Super Nintendo emulator program for x86 computers (Windows 95/98/XP).