jGameBase - jGameBase is a fully-featured retro-gaming emulator frontend and game database utility.
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Stella - Stella is a multi-platform Atari 2600 VCS emulator released under the GNU General Public License...
Mesen - Mesen is a NES/Famicom emulator and NSF player.
Javatari - Javatari is a multiplayer Atari 2600 emulator written in pure Java with no external libs.
Snes9x - Snes9x is a portable, Super Nintendo Entertainment System (SNES) emulator.