Basilisk II - Basilisk II is an Open Source 68k Macintosh emulator.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Sheepshaver - Home page of the SheepShaver Macintosh emulator
Mesen - Mesen is a NES/Famicom emulator and NSF player.
PCE - PCE is a collection of microcomputer emulators. At the moment it contains three emulators:
Snes9x - Snes9x is a portable, Super Nintendo Entertainment System (SNES) emulator.