Single Hardware

The Cinematronics Emulator
Emulates Cinematronics games under DOS and Windows 95.
http://zonn.com/Cinematronics/emu.htm

Daphne
An open source Laserdisc emulator for Linux, MacOS X, and Windows 2000/XP.
http://www.daphne-emu.com/

Galaxian Emulator
A Galaxian hardware emulator. Runs on DOS, Windows 95 and Linux.
http://galemu.emuunlim.com/

Laser - Little Arcade System Emulator Releases
An open source 8080 hardware emulator for DOS, Linux/SDL, and Windows.
http://laser.sourceforge.net/

Sideway
A freeware Midway8080 emulator (Seawolf, Boothill, Gunfight, Space invaders...) for DOS.
http://home.swipnet.se/~w-87724/arcpreserv.html

SIEmu
An open source 8080a emulator for Linux, MacOS X, and Windows.
http://www.darkpact.com/proj/siemu/

System 16 Emulator
An open source 680x0 using systems emulator for DOS and Windows.
http://www.system16.com/emu-sys16.php