jGameBase - jGameBase is a fully-featured retro-gaming emulator frontend and game database utility.
Javatari - Javatari is a multiplayer Atari 2600 emulator written in pure Java with no external libs.
Stella - Stella is a multi-platform Atari 2600 VCS emulator released under the GNU General Public License...
Mame - MAME stands for Multiple Arcade Machine Emulator.
WinUAE - WinUAE is a Windows port of the emulator UAE.
Steem Engine - Steem is an open source Atari STE emulator for Windows and Linux.