Basilisk II - Basilisk II is an Open Source 68k Macintosh emulator.
jGameBase - jGameBase is a fully-featured retro-gaming emulator frontend and game database utility.
Sheepshaver - Home page of the SheepShaver Macintosh emulator
Z26 - Z26 is one of the best emulators for the Atari 2600.
PCE - PCE is a collection of microcomputer emulators. At the moment it contains three emulators:
WinUAE - WinUAE is a Windows port of the emulator UAE.