RetroArch - RetroArch is a frontend for emulators, game engines and media players.
melonDS - A Nintendo DS emulator with support for commercial games.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
Drastic - Drastic is a Android DS Emulator
DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
No$GBA - If you have no money you can play Nintendo DS and Gameboy Advance game.