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.
Z26 - Z26 is one of the best emulators for the Atari 2600.
Mednafen - Mednafen is a portable, utilizing OpenGL and SDL, argument(command-line)-driven multi-system...
Javatari - Javatari is a multiplayer Atari 2600 emulator written in pure Java with no external libs.
OpenEmu - Console and Arcade video game emulator for macOS.