John GBA - The GBA emulator is a software program that allows you to play Game Boy Advance games on your computer.
melonDS - A Nintendo DS emulator with support for commercial games.
MESS - Emulates most gaming systems that exist, emphasizing accuracy over speed.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Eclipse emu - Eclipse is a multi-platform emulator of Game Boy Advance and Nintendo DS games.
nds4droid - nds4droid is a free, open source Nintendo DS emulator written for Android smartphones.