RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Mesen - Mesen is a NES/Famicom emulator and NSF player.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
Snes9x - Snes9x is a portable, Super Nintendo Entertainment System (SNES) emulator.
DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
BSNES - bsnes is a Super Nintendo (SNES) emulator focused on performance, features, and ease of use.