FCEUX - FCEUX is a Nintendo Entertainment System (NES), Famicom, and Famicom Disk System (FDS) emulator.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Nestopia - A portable and cycle-accurate NES emulator written in C++
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
VirtuaNES - VirtuaNES is Famicom/NES emulator for Win32.