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.
BSNES - bsnes is a Super Nintendo (SNES) emulator focused on performance, features, and ease of use.
Z26 - Z26 is one of the best emulators for the Atari 2600.
ZSNES - ZSNES is a Super Nintendo Entertainment System emulator.
Javatari - Javatari is a multiplayer Atari 2600 emulator written in pure Java with no external libs.