Stella - Stella is a multi-platform Atari 2600 VCS emulator released under the GNU General Public License...
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
jGameBase - jGameBase is a fully-featured retro-gaming emulator frontend and game database utility.
Snes9x - Snes9x is a portable, Super Nintendo Entertainment System (SNES) emulator.
Steem Engine - Steem is an open source Atari STE emulator for Windows and Linux.
BSNES - bsnes is a Super Nintendo (SNES) emulator focused on performance, features, and ease of use.