melonDS - A Nintendo DS emulator with support for commercial games.
DEmul - DEmul is a Sega Dreamcast emulator able to play commercial games.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
DreamEMU - DreamEMU is a Sega Dreamcast emulator that can play CPU Demos and homebrew games.
nds4droid - nds4droid is a free, open source Nintendo DS emulator written for Android smartphones.
Roms Mania - A working online resource for roms.