DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
Citra - Citra is a work-in-progress emulator for the Nintendo 3DS.
VisualBoyAdvance - VisualBoyAdvance (VBA) is a free software (GNU GPL) emulator targeted for the Game Boy, Super Game...
3dmoo - 3DS Emulator Prototype
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.